Recently I was disinvited from giving a commencement address at the small Liberal Arts College within Concordia University in Montreal. My speech was to be on the study of great books, to which that college is devoted. The invitation was a surprise, and the rejection less of one, because I am a white male conservative professor. Though I teach at Harvard and lecture elsewhere fairly often, I don’t get invitations for occasions when universities put their principles on display. My last commencement address was for a private high school in rural California.

My...