Nancy MacLean is a historian at Duke University and an opponent of libertarian and classical-liberal political philosophy. Critics have called her 2017 book on the subject, “Democracy in Chains: The Deep History of the Radical Right’s Stealth Plan for America,” biased and inaccurate. I don’t know enough about her work to judge its quality. But I’m angry about something she said recently.

“It’s striking to me how many of the architects of this cause seem to be on the autism spectrum,” Ms. MacLean said during a February talk...