Three years ago, historian Niall Ferguson wrote about Silicon Valley’s determination not to get caught flat-footed again when it comes to Donald Trump. “Make no mistake: 2016 will never happen again,” he warned. Zuckerberg had been personally lobbied by Barack Obama on these matters. Governments in Europe were looking for their pound of flesh too.

Suddenly, Facebook and other social networks got more active politically. They banned online ads in Ireland’s abortion referendum, which advantaged the pro-legalization side. Germany passed a law effectively siccing social-media companies on the government’s right-wing critics. While the headlines were about going after extremists and plots …