I hinted at this in the comments on my previous post, and also here. The concept of sexual orientation, as it is usually presented in the British media, is rubbish, and not only so, but unhelpful rubbish. Let me explain:
A good place to start would be the Kinsey Scale. Kinsey's report in 1948 is an important cultural turning point, especially in legitimising homosexual behaviour. But this is what Kinsey actually wrote.
Males do not represent two discrete populations, heterosexual and homosexual. The world is not to be divided into sheep and goats. It is a fundamental of taxonomy that nature rarely deals with discrete categories... The living world is a continuum in each and every one of its aspects.
While emphasising the continuity of the gradations between exclusively heterosexual and exclusively homosexual histories, it has seemed desirable to develop some sort of classification which could be based on the relative amounts of heterosexual and homosexual experience or response in each history... An individual may be assigned a position on this scale, for each period in his life.... A seven-point scale comes nearer to showing the many gradations that actually exist."
(Kinsey, et al. (1948). pp. 639, 656)
Quote from Wikipedia, not coz it's reliable but coz it's easier.
In other words, Kinsey thought that people are not split into homosexuals, bisexuals and heterosexuals, but that there is a continuous scale (if it's continuous, 7 points isn't really enough - you'd need to allow decimal points or just give it as a percentage, as Arthur C Clarke in The Songs of Distant Earth), and people's position on that scale can and does change over time and in response to events. For example, one potential (anecdotal but plausible) response to sexual abuse is to seek sexual fulfilment in different environments. So if a woman is sexually abused by a man, that may in some cases lead to increased sexual preference for women.
In fact, the scale is multidimensional as well. Some men prefer curvier women, some prefer skinnier women, and that preference can change over time (personally, I find that a lot of my preferences change depending on who I meet). Some women prefer butch guys; some women prefer more "effeminate" guys, and that preference can change over time too. Some people have random or not-so-random fetishes, and so on.
My guess is that there are as many sexual "orientations" as there are people, and that for most of us, our sexual "orientation" is constantly changing.
So then, if sexual "orientation" is actually individual, multidimensional and changing, it seems somewhat silly to split it into straight, gay or bisexual. It strikes me as much more like food preferences (except of course with the additional strong bonding element in long-term stable relationships which doesn't really happen with food). It also means that it is silly to label someone's identity by their sexual preferences at any one time. I like Chinese food, but that is not my identity. I also like Indian food, but that isn't my identity either. And food is really important to me, but it doesn't define my identity. If someone did define their identity by their food preferences, you'd worry about them. And I think it's the same with sex.
People should no more define their identity by their sexual preferences than by their food preferences.
Of course, this has a huge effect on how to present the traditional Christian understanding of sex. The usual way that I hear it presented, people draw a distinction between orientation and practice, but that leads to the response that we are calling homosexual people to a level of sacrifice we are not calling heterosexual people to. Not true. There are no homosexual people, and there are no heterosexual people. There are just people. (Maybe I just overargued that bit, but it sounded good.)
It also leads to an implicit devaluing of homosexual people by the church, and it really doesn't help the institutionalised homophobia in the church die out.
Much better, surely, to say that there are just people, and we all have different sexual preferences, and that some sexual actions (like loving sex inside male/female lifelong marriage) are good and that some sexual actions (like sex outside marriage) are bad, but that we don't expect nonChristians to obey Christian standards.
It's like banning spinach or the use of MSG in food for some as-yet-unknown health reasons. Now I like spinach and I think that MSG does often make food taste better, and I'd be upset if they were banned, but you'd be hard pushed to argue that a ban on MSG for health reasons discriminated against particular groups in society, even though Chinese cooking does use more of it than, say, Italian cooking.