...Being a Catholic of the Byzantine Rite I can surprise you and mention that there are married priests in the Catholic Church. Even in the Latin Rite there are some priest converts, e.g. Anglican, Lutheran, who are ordained in the Catholic Church while married. While celibacy, understood as "forsaking marriage for the Kingdom of heaven", has always been held in high esteem throughout the history of the Catholic Church, it is not "ontologically" necessary for a priest. This differs significantly with the question of women priests. Women can't become priestess' in the Church because it is ,simple to say, impossible (See my Post #17 with link). Is celibacy a Tradition then, or a custom? I answer thusly!
The evangelical vows of chastity (and therefore, celibacy), poverty, and obedience, are indeed part of Sacred Tradition coming directly from the Apostles, particularly the witness of St. John, the "beloved disciple", who remained celibate (and of course Christ's Bride is the Church!). However, they are not essential for the priesthood and extend to other members of the Church. In fact, many lay people in the history of the Church e.g. nuns, sisters, brothers, and others, through discernment of the Holy Spirit freely vow themselves to God under the evangelical counsels. It was only natural (or supernatural!) that from the beginning of the Church that men discerning the priesthood would be at the forefront in making these vows upon ordination. From the earliest times, bishops, who were always celibate, chose men who were celibate for the priesthood with it being the local law for many "dioceses". This discipline has developed into canon law for the Latin Church for some time now, with the laws of the Eastern Churches a little more 'lax'. For example, a man not married upon ordination in the Eastern Rites takes this vow, or if becoming a widower remains unmarried.
Don't misunderstand, priestly celibacy is practiced very much so in the Eastern Rites - just not by all priests. All monks and Religious priests are vowed to celibacy, and many, if not most, secular priests freely choose to vow themselves to it as well. A corollary for Latin Rite priests would be that secular priests do not vow poverty, whereas all Religious priests do. Also, please understand that adult men freely discern and choose to be ordained in the Church if the Church, through discernment, find them to be suitable candidates. NO ONE IS HOLDING A GUN TO THEIR HEAD!!!...
...The Catholic Church forbids no one from getting married. Well, on second thought, maybe there are special cases such as an 8 year old boy marrying a 9 year old girl. The two, having not reached puberty, would be incapable of contracting a valid marriage. Impotent people, not to be confused with sterile people, cannot marry. People who have already vowed themselves to another in marriage cannot walk away from that vow to legitimately marry another. Likewise, people who validly and freely vow themselves to God. In what way is this, any of this, "CONTRARY" to His will?
Closing on the topic of celibacy. Should the Latin Rite of the Church change Her discipline? It is for Her only to be led by the Holy Spirit, and at present, the eschatological dimension of "celibate for the Kingdom of God" witness of Her priests seems to be sorely needed in a world which knows not God. Following is from Pope John Paul's Letter to Priests for Holy Thursday 1995:
"When Christ stated - as the Evangelist Matthew writes - that man can remain celibate for the Kingdom of God, the Apostles were disturbed (cf. 19:10-12). A little earlier Jesus had declared that marriage is indissoluble, and this truth had caused in them a significant reaction: "If such is the case of a man with his wife, it is not expedient to marry" (Mt 19:10). As is evident, their reaction went contrary to the notion of fidelity which Jesus had in mind. But the Master makes use even of this lack of understanding, in order to introduce into their narrow and limited way of thinking the perspective of celibacy for the sake of the Kingdom of heaven. He thereby wishes to affirm that marriage has a specific dignity and sacramental holiness, and that nevertheless there exists another path for the Christian: a path which is not a flight from marriage but rather a conscious choice of celibacy for the sake of the Kingdom of heaven."