Former U.K. Foreign Secretary Boris Johnson recently generated outrage with comments about the burqa. In a column for the Telegraph earlier this month, Mr. Johnson joked that the head-to-toe veils made a woman look like a “letterbox” or a “bank robber.” Muslim leaders in Britain labeled the remarks dehumanizing and called on Prime Minister Theresa May to investigate “Islamophobia” in the Conservative Party. She demanded her former cabinet member apologize.

Mr. Johnson’s ham-handed humor obscured his actual argument: He opposes,...