Even to ask what causes homosexuality is homophobic if you don't ask at the same time what causes heterosexuality. We don't really know what attracts men to women or women to men. (A different question from what purpose that serves.) Many strait men (especially) can't even get this question, and will try to explain their attraction as if women's attractiveness compared to men was somehow innate, leaving no explanation for men's attractiveness to strait women. When a teenager gets lusty about a teenager of the opposite sex, the last thing on their mind is "if we do this, we may have children". On the contrary!
Homophobes keep asking "What causes homosexuality?" with a view to asking "How can we cure it?" Eugenically if genetic, through ever stricter upbringing, I suppose, if it is nurture.
I like to answer "Neither, it's a Gift from God!" just to annoy them.
Nice answer, Shuggy. I like that. And along the lines of the rest of your very insightful post, I'm brought back to something my husband said a long time ago when his sister became engaged to an African American and their parents, who he had thought were so liberal and open-minded, went completely ballistic. We went to lunch with her and her then fiance and were talking about how irrational their parents were being. Ed said, "Really, we're all a little bit racist in our hearts, unfortunately. Because until you can see a man as a man and not a black man or see a woman as a woman and not a black woman, you *are* a racist. Ron agreed and admitted that his parents were having the same amount of difficulty with him marrying a white woman.
Until we all see homosexuality as something that does not need to be fixed any more than heterosexuality needs to be, we will be living in a homophobic society. But I really think that this movie has made huge strides in moving us as a society towards that goal. It has to have, because I'm witnessing people every day who say their minds have actually been changed by it.