Without such protections, social-media platforms would have a stark choice. They could take responsibility for everyone’s posts. They would therefore place stricter limits on what we write—and we’d see a likely return to posting delays as the sites review comments. It would undermine the informal nature of these discussions.

Or they could allow anyone to post whatever they choose, which would mean that forums—especially the more freewheeling ones that conservatives increasingly seem to prefer—would be swamped with garbage, targeted attacks, incitements to violence, and the like. Anyone with an email spam folder should know what to expect.

Instead of hobbling the big tech firms that Trump and others despise, it would make them more powerful. They could afford armies of people to review posts, whereas smaller sites would go out of business or become unusable cesspools. It would open the door to endless litigation—to the detriment of everyone except for trial lawyers.