@bombastic bob - I'm well aware of the research on such matters, m'dear (I've read quite a lot of biomedical and psychological texts and research on the subject), but given some of my comments tend to the overlong, I was doing my best to keep it reasonably short, rather than write a dissertation! Well done, and have an upvote from me for a quite reasonable posting on the subject.
However, it's still true that on the whole, for most folk sexuality is not a matter of choice. If you're homosexual, the availability of potential sexual partners is much more limited than for heterosexuals, and social pressure can make it extremely hard to even locate suitable partners, never mind actually get together with them. I know that many women of my age who now identify as lesbian have been in heterosexual marriages before because they were lonely and saw no hope of being able to enter into a lesbian relationship, when they were younger. Extreme lonliness can drive one to extremes of behaviour, including going against ones innate sexuality, particularly with huge social pressure to conform pushing one in that direction. That doesn;t really equate to choice in the sense of free choice though, now does it?
The plain fact of the matter is that I'm just not terribly interested in guys that way, and that is NOT a matter of personal choice. I'm not anti-guys though, heck, some of my best friends are male... 8-} ;-}