>>If homosexuality were actually genetic, homosexuality would have ceased to exist thousands of years ago due to the fact that the gene would have disappeared through the elimination of reproduction.<<
This isn't necessarily true. What if the carriers of the gene still engaged in heterosexual, pro-creation behavior either in addition to homosexual behavior or in spite of their homosexual pre-disposition, if applicable.
I don't think it is beyond the realm of possibility to have an ingrained (or is that spelled with an "e"?) predisposition to certain forms of behavior, including homosexual behavior. But the key is to think of homosexuality in behavioral terms, because that is what it is: behavior.
So, in that case, even if it is genetic, one still has to consciously decide to engage in the behavior. Which means that a person has the ability, through free will, to not behave in this way, or even to ask God to remove the desire to commit this sinful behavior. And all of this means that there is no reason for a person to remain a homosexual if they don't desire to.