My theory: a certain percentage of people have a lower than average empathetic response, usually by birth, but sometimes also by repeated exposure to mistreatme

My theory: a certain percentage of people have a lower than average empathetic response, usually by birth, but sometimes also by repeated exposure to mistreatment/neglect at a young age. These indivduals probably played an evolutionary role in human tribes (perhaps something similar to those "soldier" ants in some ant colonies). But the scale and connectedness of modern society allows such individuals to expand their influence in ways that were not possible in prehisotric societies. And so they go ahead and do it. I don't believe they have any problems sleeping at night or looking at themselves in the mirror. Those circuits in their brains either don't function or are heavily attenuated.