Perhaps myth is too strong a word: “rarity” or “highly unlikely” might be more accurate. It is possible for a priest to have a homosexual orientation, and yet remain faithful to his vow or promise of chastity, and also support Church teaching on sexual ethics. It is possible for a lay person to be gay and yet be faithful and chaste. But given the current cultural situation and the many Catholics who oppose Church teaching on every question in sexual ethics, unfaithfulness and unchaste behavior are much more common.
Most straight Catholic laypersons do not believe or practice all that the Church teaches on sexual ethics. So we should not be surprised when gay Catholics do the same: adopting secular views on sexuality and living according to those views. These are very grave errors that do harm to the individual, society, and the Church. But we cannot have a double standard in which straight Catholics commit all kinds of grave sexual sins before and during their marriage, while gay Catholics are expected to be the only ones who are chaste and faithful.
If you are outraged at gay marriage and openly gay priests (and you should be), take a look at your own life. Consider whether you believe all that the Church teaches on sexual ethics, and live according to that teaching. Maybe you need to go to confession, before you go forth and preach against grave sins in the area of sexuality.
The problem with allowing a gay man to be a priest, under a vow or promise of chastity, is that society will constantly pressure that man to think and act according to the prevailing view on homosexuality. Any individual priest might remain faithful. But it is imprudent for the Church to allow gay men to become priests, because we can reasonably anticipate that some, perhaps many, will be influenced by society to reject Church teaching and to commit grave sexual sins. And much more harm is done when a priest commits these sins. The public acceptance of gay marriage and grave sexual sins by a priest harms the Church by scandal, and reinforces the sinfulness of the weak in faith who are already overly-influenced by secular society.
Consider the case of monsignor Krzysztof Charamsa. He has publicly expressed views which show no faith whatsoever in Catholic teaching on sexuality and ethics. He has called the Church “homophobic”, made other deplorable remarks about what is ostensibly his own religion, and he has publicly admitted to breaking his vow of chastity and to committing grave sexual sins without repentance.
He is celebrated by the mass media, as if he were a hero. The sinful culture approves of his grave sins and reinforces his heretical ideas about sexual ethics. The Church should not ordain gay men because they will constantly be under pressure from society to reject Church teaching, and to break their vow.
Worse still, if many gay priests are permitted in the priesthood, some will inevitably be promoted to higher positions in the Church. In the above mentioned case, the priest became a monsignor who worked for the Vatican, until he was discovered to be unfaithful. Much harm can be done if a gay priest, who perhaps hides his views and orientation, is promoted to Bishop or Cardinal. I have read and recommend this book: Goodbye Good Men, by Michael S. Rose. It details the depth and breadth of the problem of gay priests and seminarians.
What is the solution to this problem? It is not sufficient for the Church to forbid gay men to become priests. Any priest, straight or gay, who speaks in favor of gay marriage should be laicized and excommunicated. The Church must teach more clearly and more emphatically on every question within sexual ethics. And the faithful must believe and live that teaching. As I have written many times in previous posts, it is a grave scandal and a sacrilege that most persons who receive Communion are guilty and unrepentant from grave sexual sin. Most Mass-going Communion-receiving Catholics have rejected some, even most, of what the Church teaches on marriage and sexual ethics.
The solution to the problem of gay priests, and the problem of the wide acceptance of gay marriage by the laity, and the problems of abortion and contraception, is one and the same: every Catholic must learn, accept, and live according to a proper understanding of Catholic sexual ethics.
Please take a look at this list of my books and booklets, and see if any topic interests you.