I am curious as to why you feel that allthough genetic, having homosexual intercourse is sin? Are homosexuals damned by there genes? By either not being able to express physical love for someone they love, or damning themeselves to hell for expressing this physical love?
I would look at it as sin because I don't think in homosexual intercourse was part of God's plan for us. Sex was designed within the context of marriage between a man and a woman. And I don't necessarily think that by being a homosexual you are damned by your genes just as anybody else whos genes give them an increased predisposition to certain sins. Nobody said I'm required to have sex with my girlfriend and even if sometime down the road we get married, I'm still not required to have sex with her. I'm not sure exactly which apostles but I believe 2 of them were not married because they wanted to be able to serve God without the restrictions that come with being married. I would like to think that if I was a homosexual I would look at it the same way. I would consider it a gift of celebacy and count it gain that I could serve God more fully. And yes I cannot fully grasp how hard that would be. It obviously was pretty difficult for many Catholic priests.
Back to the being damned by the fact you are homosexual....I don't see that from these bible verses, especially verse 11:
1 Corinithians 6:9 - 11
9Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived; neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals,
10nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers, will inherit the kingdom of God. 11Such
were some of you; but you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus Christ and in the Spirit of our God.