I honestly never understood the fixation on this issue. It's sometimes phrased as 'nature or nurture' in regards to the trait.
Some folks have a lot emotionally invested in the 'nature,' but that always seemed strange and misplaced to me. That something is 'natural' isn't really all that important, nor does it validate anything.
I once had this discussion with a very passionate liberal female lawyer I used to work with. After she went on about the importance of the natural aspect. When she was done, I raised the issue of men, women, and sexual instinct. Specifically, it's perfectly 'natural' for a male to see a female, get an instinctive sexual reaction, chase her down, tackler her to the ground, and force sex upon her.
That's how it works in much of the animal kingdom. That's how primitive humans probably did it. It's perfectly 'natural' but that's not to say it's desirable or good conduct, particularly in a civilized society. She raised the objection that my example didn't factor in the female's consent.
Of course, I reminded her that there's nothing particularly natural about consent, either. While sometimes in nature the female does exhibit a willingness to mate, that's certainly not the exclusive mandate at all. She got very upset at all of this talk, but I reminded her that it was she who raised the importance and significance of 'nature' in these discussions. My personal position is that 'nature' in itself doesn't validate anything, necessarily. She got more upset and left.
Not too bright, that one. Strong self esteem, though.
I believe it's the radicals pushing the homosexual agenda that have given the nature part of homosexuality so much time in the spotlight. When you include this misinformation with GLSEN you get children experimenting with homosexual behavior. That's a really bad idea and needs to be exposed for what it is.