I'm not sure if I was clear about this in my other reply. When I say discussion of slash, my curiosity is not so much why people find the idea attractive (I'm thinking a lot about what you said about insulting people's sexuality preferences), but rather why people who defend slash on a story/character basis-- like what you said about Angel and Wes. I would find it more likely to believe in S/A than A/W as likely possibilities within the storyline given to us (though this is totally a bad example because I haven't watched near as much AtS as most everyone else in LJ), and that might be a discussion I'd want to have, later when I've seen seasons 1-3 and know what I'm talking about. See the difference I'm getting at, though? Not so much "why do you like the idea of them together", but rather "why do you feel that they are together or will be and that is how we are meant to read it"--- the latter being much more familair to me in the Gundam Wing fandom than in Jossverse. For shows like Buffy and Angel, and books like Harry Potter, I've seen in much of fandom there a well-recognized line between what we'd like to see happen /imagine happening, and what we think the writers are daring enough (or too politically correct) to do with their main characters. When I used to be in GW fandom, that line was non-existant, and debates of slash (called yaoi in anime fandom) were in the most literal sense, not the theoretical sense.
Just to clarify