Consider the following quotes:
"I think if you were to talk to Dick Cheney's daughter, who is a lesbian, she would tell you that she's being who she was, she's being who she was born as. I think if you talk to anybody, it's not choice." (John Kerry, Oct 13 2004)
"The question is, what kind of person is her father, to so hatefully oppose something that's so innately part of Maya?" (http://www.dailykos.com/story/2004/9/27/02154/0865)
It seems to me like a common opinion to hold, among those who support the validity and reasonableness of homosexual intercourse, relationships, and marriages, that sexual preference is innate. Conversely I associate people disapproving of homosexuality with the belief that it is a choice, a habit that can be made and unmade through choices and exposure to ideas and influences.
Now, if you're planning to consider it sinful, you kind of need to regard it as voluntary. If a religion considers farting a mortal transgression, that's pretty rough. I suppose I could regulate my diet or something, but if I cut loose now and then --- well, let's just say I don't feel a moral obligation or responsibility to what my digestive tract does. Even christians who regard masturbation as sinful can consistently regard nocturnal emissions as innocuous because they are involuntary. So, a reasonable-sounding theological rule of thumb is "involuntary imples not sin". Contrapositively, "sin implies voluntary". So if you're in a Levitican mindset already (and you believe in classical logic, which I think I can safely bet most of you reading do, at least more than the Leviticus-readers) then homosexuality has got to be a choice.
So it's almost as if the people on the other side of the "homo is crap sexuality" coin reasoned that they must, to stay in sufficient opposition to their opponents, believe that homosexuality is innate. This is a caricature, of course. I still find the basic idea of it a strange opinion. I feel much more sympathetic to the possibility that sexual preference is highly influenced by environmental factors and also homosexual intercourse is just as fine in and of itself as heterosexual (with all the same provisos about age, consent, consideration of diseases and so on).
Because you know what? We all already believe the big ol' capital-M Media has hornswoggled us men into liking big-boobied, blonde, shallow, slim-waisted, pouty-lipped anorexics. It's taken for granted in plenty of circles that this phenomenon is real, that our sexual preferences within one gender are practically dictacted word-for-word and figure-for-figure by magazines and movies and television.
So if exposure to various self-selected cultural influences over twenty-odd years of life can make me prefer Kathleen Hanna to Britney Spears, Audrey Tautou to Pam Anderson, and Jodie Foster to Lindsey Lohan, who's to say a moderate departure from the average cultural experience couldn't nudge someone across the gender line? I think I already have a preference for somewhat androgynous appearance in women, even if at the same time I feel a clear preference for women per se. And why not think of such nudging as just as morally neutral as the overwhelmingly contingent differences between peoples' taste in hair styles, clothing, makeup, and speech?