More than likely there is a complex set of factors involved here, and genetics are probably not the main determinant, let alone the only one. I'm learning toward hormonal conditions in utero, personally.
Full disclosure here: I am a lesbian, and have always been this way. My mother says she knew at age 4 somehow, which is odd since I had no idea there was such a thing until 14 and wouldn't admit it till 16. It's not about hating men; I actually have more male than female friends, I just don't want to sleep with them. I wasn't abused, either...but my sister was. My heterosexual sister. So there goes that hypothesis.
There are gay animals out there. I don't mean "we've observed one instance of homosexual behavior among two random members of X species," I mean there are pair-bonded gay couples all over the animal kingdom. "It's unnatural" is a stupid argument, though it's amusing how fast they switch over from that to "well we're not animals!" when the above is pointed out. Honey, yes we are, we're just very smart animals.
Any and all religious arguments are worth less than nothing, and IMO are blasphemous; they are putting words in their God's mouth. "Lifestyle factor" arguments are somewhere between disingenuous (lesbians have lower STD rates than any other group) to outright evil (of course gay people commit suicide more, society f****** hates us!). At this point it's down to people mistaking their own biases for gospel truth.
Oh well. As a wise philosopher-poet of our time once said, "haters gonna hate."