You’re very right to observe that the Jewish and Christian traditions proscribe homosexual acts, as do the other major religions, including Islam, Hinduism (at least for the “twice-born”), Buddhism, and Taoism. It’s important of course to specify “acts”—that is, sodomy in one form or another—since the orientation or tendency per se is morally neutral, though nonetheless one sign (among many) of the Fall. It’s also important to remember that from a traditional Christian point of view these acts as such are no worse in principle than fornication or adultery between heterosexuals.
And let’s not forget Christ’s words on the subject of sexual sin in general, namely, that a lustful thought is essentially—inwardly—the same thing as an adulterous act (Matt. 5:28). Given this precision, it’s surely worth asking how many people are truly guiltless in this domain. Who has not sought, and perhaps been consumed by, a few fleeting seconds of pleasurable sensation while forgetting the God-given beauty, sanctity, and sacramentality of the sexual act? How many otherwise virtuous spouses engage in intercourse in a true spirit of reverence—reverence for the God who made sex and reverence for the “image of God” who lies beside them—and without treating their husband or wife merely as a physical apparatus and occasional means?
It doesn’t follow, however—as you come close to suggesting—that the traditionalist, whether Christian or otherwise, is therefore best advised to “stop throwing stones” since his own house is “made of glass”. As long as we’re prepared to admit that we’re sinners ourselves, there’s nothing amiss in calling a sin a sin. “Do as I say, not as I do” is the refrain of everyone but the saint. No doubt it would be much easier, given the loud and often belligerent advocacy of homosexual conduct in our culture today, just to keep our mouths shut! Not to do so, especially in the academic environment that you and I share, is certainly an invitation to be labeled a “homophobe”. If and when you are, my suggestion is that you should calmly but forcefully explain (as I’ve had occasion to do) that you’re not afraid of but for all people who parade their vices—sexual or otherwise—as if they were virtues.
In any case we mustn’t end up “loving the sin” because of our rightful, indeed obligatory, efforts to “love the sinner”. I’m thinking, of course, of Saint Augustine, who tells us that we shouldn’t hate the sinner on account of his sin (as defenders of traditional precepts have too often done), nor should we love the sin on account of the sinner (as the political correctness of our times demands). On the contrary, we should love the sinner and hate the sin. As in so many areas of the spiritual life, the correct approach is a balancing act.