I sincerely feel that Ao3 should have a tag dictionary of what each tag means to cut down on mistagging. A lot of it is newbies just guessing what tags mean and having a definitive answer to what tags mean would cut down on that sharply.

As someone who also enjoys BDSM aus I do understand the frustration in people tagging it as an au for no reason.

I mean I don't know why these people are using BDSM AU tag for things that aren't a BDSM au when they don't use AU to denote everything noncanon sorry for the confusion.

I have no idea why you'd tag BDSM as an AU unless the characters in the canon explicitly are against BDSM. Otherwise it's just a tag. Do people tag Alternate Universe -gay? Or alternate universe - dating?

WELCOME TO THE DRACULA PAPRIKA DISCOURSE!!

(meme from tumblr, not my own, original link seems to be dead now)