This is really interesting, though, what you bring up, Nabu...
How do we reconcile the basically-accepted-truth that sexuality is inborn and the basically-accepted-truth that sexuality is a gradual range from completely (or effectively-completely) gay to completely (or effectively-completely) straight and everywhere in-between?
If we accept both of these things, we've got some sticky things to figure out in the gray area between them, you know?
Though the general sway of someone's sexuality somewhere in that range is pretty undisputably set in the womb... aren't we still swayed within our own range by later environmental influences?
Couldn't someone be "mostly gay" or "mostly straight" but be driven to the extreme of their range by a family or cultural influence? Couldn't someone who is pretty much down the line bisexual be pushed into almost solely exploring one side or the other, for reasons that... aren't about prejudice or fear but just their own preferences from their own experience?
Not to get too personal... but my significant lady is, in terms of preference, in terms of who she notices and what she has fantasy about... if anything slightly leaning toward the lesbian side of bi.
But with me, with this particular male, in this particular situation, she claims to be completely content and has for... seven years now. Even though she only dated girls a little bit and never got past "second base" with another lady... and she went to the gayest public college in America, SUNY-Purchase, where if anything the expectation was to be gay...
She's mostly dated boys, myself included. No one would've disowned her, she wouldn't have lost any jobs or friends... in fact, she lost some friends at college for getting long-term with a guy... but for her own internal reasons, despite being very much bi in terms of libido, she's generally been interpersonally more comfortable dating guys.
One of my best friends from high school, he is the exact opposite... pretty close to down the line bi, but most of his significant relationships have been with other men.
I don't think my girlfriend is lying to me and... I don't think my friend Adam is lying to me, either.
There's gray area between sexuality and actual sexual expression, I guess I'm saying, and there's an interplay there between how you were born and how you were influenced along the way to who you are now.
I just wouldn't wanna be reductive about it, to either direction.