It's emotionally satisfying to see assholes taken down a peg and it usually coincides with The World Being Made A Better Place™ but human suffering is bad even if it's happening to a bad person. So if we're talking, for example, Shinzo Abe getting got by some dude with a contraption, yeah it's funny because that's one less fascist ghoul and it was totally from left field for everybody. If he were instead being tortured in a basement somewhere, I would say that would not be funny to see firsthand and it's bad. If we're talking beyond idle wishing, taking part in violence, even justified violence, chips away at something deep inside you. Revenge is like throwing a tantrum; cathartic at the moment, but habit-forming and an awful habit to make. If they were a bad person, the best thing you can do is move on from them. Lingering resentment is a curse.