Whether homosexuality is congenital or not, we know that MAJOR CAUSE OF THE SPREAD OF AIDS. Even though more time and effort has gone into a campaign of public relations against that proposition. I am convinced that homosexuals are at much greater risk of contracting the deadly desease than heterosexuals. That is the issue. That is the problem. That is the undeniable fact of life, and that is the reason homosexuality is wrong, because it is a major health hazard, and is responsible for the pandemic spread of one of the most deadly and costly illnesses in the world.
To say that it is a sin is simply the wrong approach. First of all sin has relevance only to those who profess a belief in God and in Christ. And as dogmatic as Christians can be about the exclusivity of their belief systems, there are many millions who do not hold the same beliefs and to hold non-believers up to the standard of the bible is ludicrous to their way of thinking.
If you are preaching to the choir then it is relevant to say that homosexuality wrong. Still its etiology is not relevant. Even the Catholic Church has recently made a clear distinction between the sin and the sinner. Homosexuals, who are not engaging in homosexual sex, and who do not openly approve or support the activity are suitable for admission into the clergy, just as any celibate individual is. So to say that homosexuality is genetic is to beg the question that God created man in his image and likeness, which is probably the bases for the religious denial of this possibility.
All in all the Christian who purports to convince an atheist that homosexuals are sinners, is spitting into a wind that is blowing into his face. If there is a more effective way to create hostility among homosexuals toward Christianity, I do not know of it. As a Christian, I say that homosexual contact is a sin, for Christians and they will be chastened by God. If the sinner cannot learn he will be taught. As for non-believers, they have a more loathsome problem, and no matter what conclusion you may come to about homosexuals, they like all other non believers will receive their recompense.
I believe you misunderstood the Vatican document. Men with deeply-rooted homosexual tendencies, i.e. anyone who would identify as homosexual, chaste or not, are not to be ordained or admitted to seminaries.