It is quite common to expect non-Catholics, especially Protestants, to condemn the idea of an unmarried clergy. The claims have always been based on the scriptural fact that under the Mosaic Law, and up until apostolic times, priests were allowed to be married. In expectation of the coming of the Messiah under the Old Law the certified male descendants of Aaron, who became priests, were allowed to be married. And, under the New Law after Jesus the Messiah fulfilled and abrogated the Old, priests were still allowed to be married. The New Testament scriptures bear witness to this permission.
Today, there is an additional objection to an unmarried priesthood. As the world becomes more materialistic and immoral, a portion of the clergy has likewise been infected, and the Mass Media has put a magnifying glass to the individual cases of priests who are "accused" of immoral acts and abuse of minors. (There is however not much focus subsequently as to whether they were convicted). Such a specialized focus has naturally allowed people to associate the thought of "immoral crimes against children" whenever the word "priest" is mentioned! The modern objection, then, to an unmarried priesthood, is the claim that - they would not commit these crimes if they were married priests!
This last objection is quickly and easily addressed. This claim is made without thinking and without reason. Such people make the claim on the foggy and mistaken notion that ALL priests today are committing these crimes, which is hardly the case. People who passively let their minds be molded by the Mass Media will nonetheless tend to think this way.
More importantly still, there is the statistical fact of centuries upon centuries where Catholic priests have lived holy and saintly lives always with a reputation above the general populace. Any people who make such foolish claims today are not "thinking people". More likely, if their objection does not stem from ignorance and a poor use of reason, it will stem from a failing moral disposition that denigrates the practice virtue, grace, and the concept of goodness with a mind even to condemn the Church Herself even though (and this is important) these infractions are committed AGAINST the teachings and doctrines of the Church! If this same line of thinking were carried further, we should hear that the Church is bad because Judas Iscariot betrayed Christ, and maybe we should do away with holy poverty so as to prevent crimes such as Judas' where he sought to gain thirty pieces of silver for handing Jesus over! But in truth, celibacy for the clergy is no more the cause of immoral acts than was Judas' greedy act of betrayal caused by the holy poverty of the Apostles. Sin is in the evil will of the perpetrator - against the laws of God.
The same mentality that would blame the restraint and sacrifice of a whole celibate priesthood for the relatively few crimes committed would likely blame the whole system of "private ownership of property" because of the scattered crimes of theft and burglary! Or still further, why not blame the restraint of a monogamous marriage for all the crimes of adultery, bigamy and polygamy?! One can easily see the insanity, and even diabolical character, of this way of thinking.
Have these people who make claims against celibacy today ever stopped to think that it is not mere coincidence that society itself has become far more immoral in general statistically than any individual priests that can be focused in on for the news? How foolish it is to think that a life of celibacy is the cause of these immoral infractions against all contemporary and historical facts.

THE SCRIPTURAL ARGUMENT

What about the scriptural argument against celibacy? The typical Protestant will argue that St. Paul makes mention in the Bible that it is allowable for priests to be married:

"It behoveth therefore a bishop to be blameless, the husband of one wife, sober, prudent, of good behavior, chaste, given to hospitality, a teacher, Not given to wine, no striker, but modest, not quarrelsome, not covetous, but One that ruleth well his own house, having his children in subjection with all chastity." (I Tim. 3:2-4)

"For this cause I left thee in Crete, that thou shouldest set in order the things that are wanting, and shouldest ordain priests in every city, as I also appointed thee: If any be without crime, the husband of one wife, having faithful children, not accused of riot, or unruly. For a bishop must be without crime,..." (Titus 1:5-7)

What can we say of those people who would point out these biblical quotes, shut the book, and insist that priests should be married because, "That is the way it was in scripture."? What should we say of these same people who apparently do this while closing their eyes to the context in which it was written, ignoring the other quotes within the same Bible which qualify its meaning? The least that could be said is that such people have a very poor reading comprehension.
It is quite clear even within the context of the very sentences that St. Paul wishes to insist that priests be faithful, chaste and not adulterous, "the husband of one wife". This by no means implies that he MUST be a husband, but that he must NOT have more than one wife which is being chaste and upright.
Catholics, however, know that all the teachings in the Bible must be taken as a whole. While St. Paul simply accepted the fact that a priest could have a wife, he at the same time was divinely inspired to express the will of God in regard to whether the married state was the preference or not. St. Paul himself being unmarried, said in his first letter to the Corinthians (chapter 7):

"For I would that all men were even as myself: but every one hath his proper gift from God; one after this manner, and another after that. But I say to the unmarried, and to the widows: It is good for them if they so continue, even as I..."

"Now concerning virgins, I have no commandment of the Lord; but I give counsel, as having obtained mercy of the Lord, to be faithful. I think therefore that this is good for the present necessity, that it is good for a man so to be....Art thou loosed from a wife? seek not a wife..."

"But I would have you to be without solicitude. He that is without a wife, is solicitous for the things that belong to the Lord, how he may please God. But he that is with a wife, is solicitous for the things of the world, how he may please his wife: and he is divided. And the unmarried woman and the virgin thinketh on the things of the Lord, that she may be holy both in body and in spirit. But she that is married thinketh on the things of the world, how she may please her husband....But more blessed shall she be, if she so remain according to my counsel; and I think that I also have the spirit of God."

Indeed St. Paul did have the spirit of God; he repeats the teaching of Our Lord in the Gospel in regard to celibacy:

"He that can take it, let him take it." (Matt. 19:12)

Catholic teaching is clear: marriage was scripturally allowed for priests and marriage was taught as being good, but the unmarried state was counseled as being the better state in life - more blessed spiritually and more efficacious for the ministry. Is it but natural and good to follow this counsel and encourage people in the same manner as did Christ and St. Paul? Of course. And the followers of Christ took this counsel well. It was voluntarily followed to such and extent by the ordained priests and bishops of the first few centuries that by the time the fourth century had arrived most priests had listened to the counsel of Christ and remained celibate.
By the end of the 4th century the authorities of Christ's Church saw this trend in following the counsel of Christ, recognized the working of the Spirit, and experienced ample proof that indeed those who did so were "more blessed" and their ministries excelled because they were "without solicitude". The Church then decided officially for the western portion of the Church that all men who voluntarily decided to become priests would also have to accept the requirement that they remain unmarried. Generations upon generations have done so, and the benefits have proven to be exactly as St. Paul mentioned.

ANOTHER OBJECTION?

Protestants will object to all this saying such things as:

"If Christ intended celibacy to be a rule for priests, He would have commanded this before he ascended into heaven! But it wasn't commanded!"

Apparently such people forget that human nature rebels at big, sudden changes. Man often times needs gradual preparation for a change by undergoing a transition period. Scripturally this is exactly the process practiced by Jesus Christ and the apostles. Where a transition could be made, it was made. Obviously, the truth of the "Real Presence in the Holy Eucharist", for example, is not something that could be given gradually, so the followers of Christ were told bluntly:

"Amen, amen I say unto you: Except you eat the flesh of the Son of man, and drink his blood, you shall not have life in you....For my flesh is meat indeed: and my blood is drink indeed."

Many of his disciples murmured at this saying, "This saying is hard, and who can hear it?" And, "many of his disciples went back, and walked no more with him."

However, celibacy for the priesthood is something that could easily be implemented gradually by a period of transition. After living in a society where it was a perfectly acceptable fact for priests under the Mosaic law to be married, one can only imagine what would have happened were the command to be given so abruptly and without necessity forbidding all priests to get married! It goes without saying that the Lord knew fallen human nature perfectly. There was no necessity to make such a sudden change because marriage was not an evil. Under the Old Law, the law of fear, such a thing as celibacy could not have been supported. We know this because the Lord even tolerated divorce under the Old Law for certain reasons, as He said, "Because Moses by reason of the hardness of your heart permitted you to put away your wives: but from the beginning it was not so." (Matt. 19:8)
The Old Law of fear was replaced with the New Law of grace, enabling men to live in the state of celibacy if they were called by God to take it. But to have imposed celibacy on the priesthood immediately would have been counterproductive especially because marriage was always a good thing in itself.
We see many signs of gradual transition when it comes to the Mosaic Law. The Bible is full of problems which inevitably arose among Jews and Gentiles. Judaism was the true religion which was abrogated/fulfilled by Christ. The "People of God" were no longer exclusive to the Jews but were all men who accepted the teachings of Christ, were baptized and submitted to Church authorities. The transition period was filled with difficulties, and Jesus Christ left it to his Church to grapple with the decisions involved with the help of the Holy Spirit. For instance, the Lord did not Himself decide whether his followers would continue to be circumcised or not, or whether only Gentile followers were exempt. The difficulties and trials were many, and lasted many years, and the works of the Old Law were gradually done away with over the years. The New Testament scriptures are filled with these issues.
These changes implemented by the authority which Christ gave the apostles. We see one of these changes made by the apostles in the Acts of the Apostles (ch. 15:28) where they do not hide their authority for their decision regarding the Mosaic Law:

"For it hath seemed good to the Holy Ghost and to us, to lay no further burden upon you than these necessary things: That you abstain from things sacrificed to idols, etc."

Our Lord Himself makes it clear to his disciples that they would have this power to make further changes for His Church which the Spirit of Truth would have to show them because they could not bear it yet at that time:

"...it is expedient to you that i go: for if I go not, the Paraclete will not come to you; but if I go, I will send him to you. And when he is come, he will convince the world of sin, and of justice, and of judgment,...I have yet many things to say to you: but you cannot bear them now. But when he, the Spirit of truth, is come, he will teach you all truth. For he shall not speak of himself; but what things soever he shall hear, he shall speak; and the things that are to come, he shall shew you." (John 16:7-14)

It has been the practice of the Catholic Church from the beginning to make such decisions in the very words that the Apostles used, as Church documents bear witness - "it hath seemed good to the Holy Ghost and to us..." It was just such a decision which Christ's Church made in the latter half of the 4th century which only pertained to the handful of men who were called to the life of priestly celibacy. And such a decision was well accepted because, as already mentioned, it had already become the accepted practice to follow the counsel of Our Lord and St. Paul in Holy Scripture. Who can say they accept and follow Holy Scripture and still not recognize that by the Lord's own words, there were to be changes made by the Church with help of the Holy Spirit? Who can deny it historically or even scripturally that it was up to the apostles to make transitional changes in regard to the Mosaic Law that Christ himself did not verbally tell them to make?

WHAT DO WE SAY TO THOSE WHO REFUSE TO SEE THE REASON AND PROOF

After all this, there will still be those who will refuse to see the reasonings involved with this issue and insist with the same old line - "Priests were allowed in scripture to be married, so they should be allowed today!"
The point can be gotten across in a different manner. One can use what is called the "argumentum ad hominem". Ask them if they believe that we should have slavery today. Maybe even with a touch of horror they will inevitably answer "NO!". Agree with them, but remind them here that slavery was allowed by St. Paul in the Bible:

"Let every man abide in the same calling in which he was called. Wast thou called, being a bond man? Care not for it; but if thou mayest be made free, use it rather. For he that is called in the Lord, being a bondsman, is the freeman of the Lord. Likewise he that is called, being free, is the bondman of Christ." (1 Cor. 20-22)

"Servants, be obedient to them that are your lords according to the flesh, with fear and trembling, in the simplicity of your hearts, as to Christ....Knowing that whatsoever good thing any man shall do, the same shall he receive from the Lord, whether he be bond, or free. And you, masters, do the same things to them,..." (Eph. 6:5-8)

"Servants, obey in all things your masters according to the flesh, not serving to the eye, as pleasing men, but in simplicity of heart, fearing God." (Col. 3:22)

In addition, there is the Epistle of St. Paul to Philemon. Without quoting the 25 verses of this short letter, we see that St. Paul had converted a runaway slave called Onesimus and sent him back to his master, encouraging this master to receive the repentant servant as becoming a profitable one. In all these quotes it is clear that St. Paul respected the rights of the master to have such slaves, while at the same time encouraging masters to be good to their servants (and even set them free) while commanding servants to accept their calling as slaves for the love of God.

THE POINT TO BE MADE

If anyone insists that priests of today should be allowed to marry because priests of apostolic times were allowed, they must also say slavery should be allowed today because slavery was allowed in apostolic times!

This is to maintain logical consistency. But in truth, the issue of a married priesthood and the issue of slavery have their parallel in scriptures. The New Law of grace and truth brought with it certain changes. Both slavery and a married priesthood were allowed but they were both discouraged, and their opposite praised as the ideal. They were two systems that needed to be done away with, but needed to be done away with gradually.
We have already seen why the married priesthood needed this gradual transition, and the system of slavery needed it for the same reason - namely, to prevent an unnecessary abrupt change which human nature tends to rebel against. Up to the time of the apostles, slavery was deeply integrated into the life, culture and economy of civilized man. It is estimated that more than one-third of society participated in such a system. To have immediately condemned such a practice as evil would have been too much of a shock for the average person. It must be emphasized here that if slavery WAS intrinsically evil, it WOULD HAVE been condemned unconditionally from the start. But because slavery is not intrinsically evil, the circumstances allowed for Christianity to lead the way in slowly ridding the world of slavery.
At this point, the Protestant may insist that St. Paul allowed for servants but NOT for slaves, as if there is such a distinction between the two as to make the servants nothing but ancient forms of employees! The wording and context, however, clearly show that these men spoken of are not free to go as they please, but are subservient to another man as being "called" to that state in life as if permanent and beyond their control. This is a certain characteristic of slavery.
A non-Catholic at this point may strongly object to the idea that slavery is "not intrinsically evil". This may be because the notion of "slavery" impressed upon the modern mind involves thoughts of Negroes in chains being kept in filth, with barely any clothes and beaten like animals. Such extreme abuses within the system of slavery existed here and there but were not essential to the concept. The essence of slavery is the subjection of one human to another such that the person is not free to go where he chooses, but must obey orders and cannot freely leave the state of subjection. Many servants have been kept in such circumstances, serving their masters in complete freedom, health and happiness within an estate, being highly educated, and even venturing within society for business purposes and necessary errands.
People do not think of it, but this character of submission is found in the submission of a child to his parents. A 15 year old is not free to go where he pleases and must, before God, obey all the orders his parents give him, and can even be physically corrected for infractions. This is not called slavery, of course, because it is in complete accord with the natural law, but it does show that the submission of one human to another is not intrinsically evil. Slavery on the other hand is not entirely opposed to the natural law, but nevertheless is incompatible to a degree with the dignity of a person who is a potential child of God. Calling slavery "not intrinsically evil" is not to advocate that it is acceptable in this day and age to suddenly force someone into servitude. How the system of slavery started is not discussed here as it is an undocumented complication of historically defunct cultures of old living largely in an atmosphere of continual personal survival where sometimes servitude was brought on by the settling of just debts or punishment for war, and at other times simply cruel and unjust domination for power and money. Nevertheless, it is Church teaching that slavery is not intrinsically evil.
Thanks to Christianity, the New Law of Grace and Truth, it was the Will of the Spirit to move men by doctrine and invisible grace to gradually accept and implement a celibate priesthood while encouraging all masters to free their bondsmen and accept them as brothers in Christ.