The problem comes from no concise answer as to when a zygote becomes a human. Chances are that if you use the religious view point about when we evolve into a human, you are more than likely going to believe no one is born gay. If you use science to determine when a zygote is a human being entitled to rights, you will have already accepted the numerous studies that show homosexuallity to be a naturally occuring part of nature.
The problem I have with the first approach is that the religious actually pretend they know more about homosexuality than the doctors, scientists, and the homosexuals themselves.
I don't mind giving someone the benefit of the doubt on occasion but I refuse to give them the benefit of rediculousness, ignorance, or arrogance.