Even the best of us have certain psychological mechanisms that can suddenly kick in and turn us into monsters. That to me is the basic message of events like the rise of Nazism, the Salem witch trials, and so on: not that bad people do bad things, but that good people do bad things. It's distressingly easy for those mechanisms to be triggered, either consciously by demagogues, or naively by people who think they're trying to do the right thing. Which is why I think it's more akin to tic-tac-toe.
