Many liberals, but not conservatives, believe there is an important asymmetry in American politics. These liberals believe that people on opposite sides of the ideological spectrum are fundamentally different. Specifically, they believe that liberals are much more open to change than conservatives, more tolerant of differences, more motivated by the public good and, maybe most of all, smarter and better informed. The evidence for these beliefs is not good. Liberals turn out to be just as prone to their own forms of intolerance, ignorance and bias. But the beliefs are comforting to many. They give their bearers a sense of...