I don't write "slash." That is, I don't take characters who are canonically straight and make them gay just for giggles. I don't have anything against Harry/Draco in principle, but (a) while Draco is kind of ambiguous, it's pretty clear from the books that Harry liked girls, and (b) they hated each other! So that's why I consider most Harry/Draco slash stories to be stupid. Don't even get me started on Harry/Snape.
Also, I personally don't like most "slash" stories for the same reason I don't like PWP; I want to read (and write) a story, not just an excuse to throw two characters together for hot fictional character-on-fictional character action. Most slash stories (in fairness, most "ship" stories of any kind, slash or het) are just fluffy bits of authorial indulgence. Which is perfectly fine, for those who are into that kind of thing, but that's not me.
That said... I think the idea of having to "warn" for "slash" (i.e., "Oh no, if you read this story you might be exposed to Teh Gay!!!!) is stupid and offensive.
I'm not going to take a sudden left turn into slash fantasy, okay? But, there will be gay characters. (And any gay characters you see, I assure you, were planned from the beginning, not because I suddenly decided to make a character gay on a whim -- just in case anyone accuses me of "pulling a Dumbledore.") If that offends you, you should probably stop reading my stories now.
(Yes, this rant was directly inspired by yet another dose of stupids on MNFF, but it's not the first time I've seen the issue come up.)