When groups of people who largely agree on an answer to some pressing moral or political question debate the issue together, they don’t tend to moderate or split the difference; on the contrary, they tend to egg each other on. In a surprising number of cases, they come to a conclusion that is more radical than that initially embraced by any individual member of the group. This is what the eminent Harvard behavioral economist Cass Sunstein has termed “the law of group polarization”: after groups of like-minded people have a chance to deliberate about some question of morality or politics, the
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