Most U.S. universities seem determined to harm themselves in the name of identity politics, but could they stop where their own campuses end? Harvard is now commencing a political purge of its independent “final clubs,” with troubling implications for freedom of association.

Some of Cambridge’s undergraduate clubs—akin to Yale’s societies, Princeton’s eating clubs or less rarefied fraternities and sororities—date to the 18th century. For 225 years, no one realized that these historically single-sex social organizations were...