I’M IN THE WALL STREET JOURNAL: When Digital Platforms Become Censors: Facebook, Twitter, YouTube and other tech giants say that they’re open forums. What happens when they start to shut down voices they consider beyond the pale?

Call 2018 the “Year of Deplatforming.” The internet was once celebrated for allowing fresh new voices to escape the control of gatekeepers. But this year, the internet giants decided to slam the gates on a number of people and ideas they don’t like. If you rely on someone else’s platform to express unpopular ideas, especially ideas on the right, you’re now at risk. This raises troubling questions, not only for free speech but for the future of American politics and media. . . .

Now these companies are trying to have it both ways. They take advantage of the fact that they are not publishers to escape responsibility for the endless amounts of problematic material on their sites, from libel to revenge porn. But at the same time, they are increasingly acting like publishers in deciding which views and people are permitted on their platforms and which are not. As a narrow matter of First Amendment law, what these companies are doing will probably pass muster, unless some federal court decides, as in Marsh v. Alabama (1946), that their platforms are functionally equivalent to “company towns,” where the public square is privately owned.

As a more general issue of free speech, however, the fact that a few corporations can play such a disproportionate role in deciding what subjects are open for debate is a problem. It is made more so by the pronounced leftward leanings of the big tech companies, which lately appear determined to live up to the right’s worst fears about them. Extremists and controversialists on the left have been relatively safe from deplatforming. . . .

The notion that Silicon Valley megabillionaires are actively limiting what ordinary Americans can talk and write about is likely to produce a backlash. The tech industry’s image has already suffered over revelations about Facebook’s experiments aimed at manipulating users’ newsfeeds to test their emotional states, as well as various cases of invasion of privacy and data mishandling. Twenty years ago, most Americans saw Silicon Valley as liberating; now it seems to have gone from the hammer-wielding woman in that famous “1984” Apple commercial to the Big Brother figure up on the screen.

And then there is the competition angle. Mr. Jones’s InfoWars is itself a media operation, in competition not only with Facebook and YouTube but with cable channels like CNN and MSNBC, which have made him a target. What happened to Mr. Jones could be described as “a conspiracy in restraint of trade,” in which one group of media companies gets another group of media companies to knock off a competitor.

One of the arguments for leaving tech industries unregulated has been that the industry is in constant ferment. But with a few companies now dominating the field, that ferment is less likely to continue. When giant companies combine to kick out their competitors and start interfering in politics, you can be sure that, even if they claim they are acting in the interests of decency, that’s not where it will end.

I think the Antitrust Division at Justice should be investigating the — admitted — collusion between these media companies as they shut out other media companies. It’s basically the blue-check media against the alternatives. (Bumped).