I didn't read the entire thread, but from what I did read I got the impression that the question is whether homosexuality is nature or nurture. In part of what I did read someone mentioned that roughly ten percent of the human population is homosexual, depending on the source. What nobody seemed to have mentioned though is that not only does ten percent of the human population have homosexual tendencies but ten percent of all animal populations also exhibit homosexual tendencies; the most prominent is probably bonobos. I would think that this would show that nuture plays a very small role in determining homosexual orientation (there are most likely cases in the human population that arose due to nuture but probably not many).
There doesn't necessarily have to be a "gay gene" in order for the origin of homosexuality to be developmental. It's been found that the size of areas in the brain that control sexaul arousal vary between the sexes and that in gay men these areas are the same size as in females (see, "Sex and the Brain" by David Nimmons, Discover Vol 15 No. 3 March 1994). It doesn't necessarily mean that the cause is genetic, but it is possible.