The person who has studied this the most closely, a Stanford political scientist named Morris Fiorina, has noted that if “one thinks about polarization in terms of positions on specific policy issues, one would expect to see a decline in the center and a lumping up of people on the extremes. We do not have long time series of attitudes toward particular policy issues since they rise and fall on the national agenda, but on most issues, attitudes continue to cluster in the middle rather than lump up on the extremes.” It leads to a fascinating insight. We are becoming angrier and more polarized not because of increasing issue disagreement but because we are increasingly participating in groupthink. When all the people you know, when all the people in your political sect agree with you, it becomes easy to relax in the certainty that you and your cohort are right, and the other side is not just wrong, but also taking a long, slow bubble-bath in the sea of craziness. When we don’t know the other side, when we don’t hear from them, when we don’t talk to them, when we can demonize them to our heart’s content, there are just no brakes on our sense of self-righteousness. Polarization is increasing because polarization is increasingly easy.