People often think they have mic-dropped utilitarianism by saying things like, "Oh, so if two people get a lot of joy by beating up a third person, that is ethical because it is overall net positive?"

A few things wrong with that. First is there is no net happiness formula which utilitarians are proposing. Peter Singer has said more than once that he weights suffering far, far higher than happiness.

Second is that every ethical system has screw cases which make the system look messed up. "Do unto others..." it terrible if you are talking about masochists.