I agree that it most likely has little or nothing to do with genetics, but I also doubt that many of them have much of a choice in it. There are a great many homosexuals who desperately want not to be gay and even go so far as to marry and have families in an effort to be straight. If it were just a choice these men could make then they definately would not be gay.
Homophilia (attraction to memners of one's own gender) may not be a choice; homosexuality (sexual relations with members of one's own gender) is. That said, even homosexuals culpability for their own sins may be somewhat lessened (but by no means eliminated!) by compulsive or addictive disorders.