And what happens once is likely to happen again. After this, there’ll be pressure to get Facebook, Twitter and other companies to suppress other speech, such as fiery rhetoric against the police or oil companies or world trade authorities. People will demand: If you blocked A, why aren’t you blocking B? Aren’t you being hypocritical or discriminatory?

Consider, too, that the app for Parler, a social network popular with Trump supporters, was removed on Saturday by Apple and Google from their app stores, and blocked by its hosting company, Amazon Web Services, because of concerns that some of Parler’s users were inciting violence. Merely refusing to forbid certain speech, much of which is constitutionally protected, is now a basis for blacklisting.

Companies, moreover, are run by humans, subject to normal human failings. Mr. Trump’s suspension may have been motivated by a sincere desire to resist efforts “to undermine the peaceful and lawful transition of power,” as Facebook’s chief executive, Mark Zuckerberg, put it. But other politicians might be suspended because their policies are bad for corporate profits or contrary to the owners’ political ideologies.