An unhappy side effect of the digital age is “cancel culture.” Anyone with an attitude of moral superiority and a Twitter account can try to shut down an event where opinions he dislikes are likely to be spoken. For several years the National Association of Scholars has inveighed against this infantile form of protest, which undermines free expression of ideas and legitimate debate. Now the cancel caravan has arrived at our door.

We are holding a conference co-sponsored by the Independent Institute in Oakland, Calif., in early...