Following Paul who said wished those to whom he was writing were, like he, unmarried (1 Cor. 7:7–9), Paul said he thought celibacy was the more perfect state (1 Cor 7:28), noting that "[t]he unmarried man is anxious about the affairs of the Lord, how to please the Lord; but the married man is anxious about worldly affairs, how to please his wife" (1 Cor. 7:32–33). An unmarried man is concerned about the Lord’s affairs—how he can please the Lord.The holiness of marriage makes celibacy precious; for only what is good and Holy in itself can be given up for God as a sacrifice. Just as fasting presupposes the goodness of food, celibacy presupposes the goodness of marriage. To despise celibacy, therefore, is to undermine marriage itself—as the early Fathers pointed out.
This was taken up especially by monks, who came to be respected for their lack of worldliness (let's be honest, it's more difficult for the vicar with a wife and even more, even if he's good and his wife is good, there are always tongues wagging "ooh, she wore a nice dress, where did she get THAT money from?" -- and 1500 years ago, people were the same!
And it became traditional discipline until the Council of Trent which decreed that marriage after ordination was invalid.
In this case of Paul’s personal (he labels it as such) advice and observation on the advantages of singleness it was always voluntary and marriage in no wise was a disqualification, either before or after ordination, for any office.
In fact, Paul wrote to Timothy that “forbidding to marry” was a “teaching of demons”. (1 Tim. 4:1-4)
That the “rule, discipline”, whatever it is called, is a rotten tree we need only examine it’s fruit.
By the time of the reformation the gross immorality of the clergy in general was a well known and reported upon scandal as historians like Lea and Schaff wrote about.
Said the above Schaff concerning the enforced celibacy,
“The Roman pontiff’s ordinance, setting aside an appointment of the Almighty, was one of the most offensive pieces of papal legislation and did unspeakable injury to the Church.”
(Shaff’s History of the Christian Church, vol. V, pg. 808)
500 years and a couple of billion dollars later the tree is still producing the same rotten fruit.
You say,
“To despise celibacy, therefore, is to undermine marriage itself—as the early Fathers pointed out.”
Then one must ask the simple question:
What sort of taint has been given to the whole idea of a celibate clergy by the Catholic Church’s harboring, protecting, excusing it’s most corrupt members? What sort of despising has the Catholic Church it’s self produced? What sort of undermining of marriage thereby?