Sexuality and weight
As a (largely) straight and (reasonably) thin person, I don't personally have a dog in this fight*, but Ampersand's discussion of the comparison between obesity and homosexuality (part 1, part 2) has been an interesting read. Both gays and the overweight are essentially sanctioned targets of discrimination in this society; both are most often attacked as (bad) choices and defended as genetics.
Strangely, despite their similar circumstances, there's a vast disconnect between the two -- it's not often someone's attitudes and comfort levels toward both homosexuality and obesity are the same. Overweight people can be vicious gay-baiters and gays can be among the cruelest of size elitists.
But are homosexuality and obesity choices? Yes? No? Both or neither? Ampersand's take on the subject is a thoughtful one, and some of his commenters hit it spot-on. It seems to me this comment to the first post was the money quote: "The ability to alter their sexuality or weight may vary based on how they arrived at that point to begin with."
I know people who couldn't be straight; I know people who couldn't stay thin on a starvation diet (which is a bad idea, anyway; see the discussion). I also know people who have chosen to be gay and who are naturally thin but have let their weight rise through poor diet or carelessness (oddly, people who want to be fat seem to be either invisible or nonexistent).
Neither case can be simplified down to "it's a choice" or "it's not a choice". The simplest model that fits actual, observable reality in both cases is "by genetics/by choice/not" -- or put more smartly, Brad Hicks' deviants/potential deviants/compliants.
The other interesting point about the gay/fat comparison is that it may point us to a future phenomenon. Gays, right now, are gaining cohesion and visibility -- fighting to marginalize gay-bashing and homophobes. But there's very little similar movement from the "overweight." And yet, with the parallels so strong ... if gays are successful in gaining more traction, is Size Pride going to become a force to be reckoned with within our lifetime?
* Of course, I do have a deep interest in it -- as many of the people who I respect are gay, overweight, or both, and as I think society would be better off if we could actually respect everyone instead of sanctioning people who it's OK to take cheap shots against.