Yeah "luigi says kill X guy" is stupid, but dark humor is the subtiles art of pushing stereotypes at the extreme to mock them, provoking the effect of shock in the other person, then make them laugh because it's oblivious that you're kidding
Because racism isnt exactly dark humor. It gets kind of annoying seeing all he 9/11 memes as well as the occasional sex memes like bro guve me jokes about people dying or something