i mean, i get that it's attempting to appeal to one's aversion to a very bad idea, but random bob can't cause a genocide. a strong dictatorship a la hitler or stalin on the other hand... well, that's a much bigger problem than trying to regulate mean words.
If you're a member of the subject group, then they most certainly are. Instead of constructing silly examples, let me suggest you look into the history of ethnic cleansing in Yugoslavia or Hutu-Tutsi animus in Rwanda.
invoking real world violence as a stand-in for which one calibrates their regard for a person's tweets seems more like an emotional appeal rather than a logical dialog.
Another reason not to leave it up is because it's frightening to the subjects of such eliminationist discourse, who shouldn't have to put up with being considered acceptable targets for systematic violence.