On the principle that the First Amendment exists to protect unpopular forms of expression, the American Civil Liberties Union successfully defended the Nazis’ right to march in Skokie (by the time the legal drama played out, the Nazis decided to take their parade elsewhere). That was a different world than the one we are living in today. While fear of government censorship still exists, the globe’s digital behemoths — Facebook, Twitter, Google, YouTube — possess more unchecked power and technological capability to suppress speech than any government. When it comes to Facebook, Mr. Zuckerberg in 2019 gave an impassioned defense of free expression to an audience at Georgetown University. Two years later, Facebook’s quasi-independent Oversight Board is chastising the social media giant for indefinitely suspending former President Donald Trump for allegedly encouraging violence during the Jan. 6 “Stop the Steal” rally at the U.S. Capitol. The board upheld the initial ban but punted the ultimate decision on whether to reinstate Mr. Trump back to Facebook, which the board said must make a decision within six months.