Any institution that aspires to get at the truth needs a process for testing what it believes to be true. Central to the judicial system, for example, are lawyers challenging their opponents’ arguments. In science, claims must be peer-reviewed, and experiments have to be replicated. But in politics and culture, any kind of rule-based, civil testing of facts is a fading art. Debates are hostile, ideologies harden, and we kick up a lot of dust, in which the pursuit of truth gets lost. But...