The reason I object to "slash" being used in nonfanfiction contexts isn't because I think the fans are being disrespectful to the author.

Oooooh. I finally get what you're talking about! Yes, I agree. Joss Whedon didn't write a SLAHS relationship between Willow and Tara, he wrote a lesbian relationship. What we call it in fanfic should not, imho, have anything to do with what he did.