Whether genetically based or "epi-genetically" based, I believe that most homosexuals same sex urges have their origins if not in the womb, then in early childhood. Nonetheless, I am not arguing that point. I am simply saying that even if that is true, it does not legitimate the behavior. One could equally argue that our murderous urges have their basis in our "reptile brains" (the limbic system)--that does not make them morally acceptable. We are born with proclivities to sin--for some, the proclivity to sin may include homosexuality. Being "born that way" only demonstrates our fallen nature, not our God-given nature.
If you checkout the genetics and ex-homosexual categories, you'll soon realize environment is key to this cultural issue. There are some great books on the subject as well - I just need to update that part of the database.