PRESIDENT TRUMP’S exile from Twitter and Facebook last week left him with Parler, a fringe, laissez-faire social media site, as his likely best alternative for online communication. Then Parler found itself on the outs, too, booted from Apple and Google’s app stores and Amazon’s Web-hosting service.

Mr. Trump and his followers say they are victims of anti-conservative discrimination. Their complaints are unconvincing. It is legitimate for corporate actors to scrub their sites of speech with the potential to cause harm, such as the explicit plotting that preceded last week’s armed insurrection at the Capitol. In fact, we should expect them to take such action and more promptly than they did in this case: Rule violations had, in many cases, been occurring for years, and it was only when the online harms spilled into the offline world that firms punished the perpetrators.

All the same, their response has revealed the tremendous power that a handful of private companies wield over the public square. Some of those companies are well known to the public (one, Amazon, is led by Jeff Bezos, who also owns The Post). Others operate the hidden infrastructure of the Internet and are unfamiliar to most of us. In neither case is the problem likely to be solved by familiar antitrust remedies such as corporate breakups. When it comes to operating the Web, network effects can mean a bigger business is better for consumers, which means we will never see 50 app stores or cloud-computing hosts. Instead, the situation must be tackled head-on, in the same manner this nation has tackled utilities in the past: through regulation.

The government has abdicated its responsibility on both ends of this question. There’s the matter of ensuring safety by requiring that companies put into place systems for rooting out illegal behavior, instead of ignoring or encouraging it. If we want rules of the road for the Twitters and Parlers of the Web — rules about inciting violence, for example — they should be set by our elected representatives, not unelected CEOs. And if we want those rules to be enforced fairly, without targeting speech that is merely unpopular, then we should insist that companies put into place systems for transparency, notice and appeal for their decisions. There’s good political reason to do this, as those complaining today about censorship are likely to turn tech bias into a boogeyman for voters. But there’s good policy reason, too: The public should be able to judge platforms on the clarity of their terms of service and the consistency of their enforcement.

These companies are recognizing their responsibility for shaping our discourse and our democracy. Some will say this puts us on a slippery slope toward unacceptable curtailments of expression. They’re right, but the alternative is violent rhetoric left unchecked, which we now know too well can result in violent action. It’s time for the public to insist that the government do its job and set some rules that balance the urgency of free speech with the necessity of public safety.

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