Imagine getting this pressed because someone who isn't white drew themselves as a character they did like. Art is all about personal expression and if someone wants to re-imagine themselves as someone or something they idolize then just let them do it.
I can't imagine this was the doing of the alt-right/ kkk thou, I feel like they really arent the ones that would indulge themselves within the community that this sort of artist adheres to. Most of the time in this sort of situation it's die hard fanatics of the show/movie/etc that get this enraged when they see their character changed in a way they dont like. Kinda like when the tumblr community bullied that girl to near death because she drew a Steven universe character skinny when the character was originally fat.