So just because some dickheads on 4chin decided to take shots at trans people, no one's allowed to use a word that has nothing to do with them anymore?

Sorry, but that's dumb.

Regardless of the origins, the word/context clearly doesn't refer to trans people when people call characters traps. It's use is far more widespread than some edgy little corner of the internet. I'm pretty skeptical about this specifically being the reason why some frown upon it too – most people, regardless of opinion, probably don't know about it's history. Most of what I've seen from anti-trap people has more to do with how it's used to talk about trans people rather than the history. And we're talking about a literal word in English here. The slang fits what a trap is by definition.

A small part I forgot to add since KYM can't be bothered to have an edit button:

I'm not saying that it's ok to use trap for every person/character. I agree that, in the context of a trans person/character, it's bad to call them a trap. But in the context of an anime crossdresser, it's perfectly fine to call them a trap.