Just a random thought. Do you ever wonder that the reason we like slash so much is that it's got nothing to do with us? I mean we may relate to the characters, and love getting inside their heads, and seeing these perfect (or not so perfect)relationships coming to fruition (no pun intended), but there is less chance of self-identification. The porn is hot in a more voyueristic sense, but there are other bits coming together that aren't - well - ours.
We may identify with Rodney McKay or with Blair Sandburg, or whoever, but it's not quite the same as how a lot of fangirls identify with Hermione Granger or Willow Rosenberg. Or is that a flawed assumption?
I like NC-17/R/Adults Only rated stories, but sometimes, I just skim over that part for the plot/relationshp/other stuff. I like some hurt/comfort, stories with twists and such, things that show the relationship developing.
So maybe it's not the sex thing - is it because their are a marginalized/minority group in society, and that we relate, or want to relate to that? I don't know. I can sometimes become irritated when it seems like everyone in a particular universe is gay and seems mostly paired off, like het has become a bad word... I want some sort of balance, amybe an idealization where there is het, and slash (or femslash) and it's all good. i don't mind coming out stories, or stories where they have to struggle with prejudices and such, but I do want them to overcome those struggles...
*shrugs* I'm queer-identified (bisexual, kinky, polyamorous, etc. and have had relationships with women as well as men), but I don't know how much that influences my preferences in fanfic, since I know a lot of straight girls in fandom with the same reading lists.
This is all very rambling, but I don't know, just something I was thinking about.