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SOME OF the people can be fooled all of the time, and some seem plenty pleased about it when it gives them license to exercise their most malicious impulses. How else to explain the noxious torrent of vitriol, venom and threats trained recently against a popular upper Northwest Washington pizzeria, which has been the subject of ludicrous conspiracy theories alleging that it is the center of a child – abuse racket run by Hillary Clinton and her campaign chairman, John Podesta?

The allegations against Comet Ping Pong, reported by the New York Times, are absurd on their face and detached from any gossamer thread of fact. They took root in the dark crevices of the Web and took flight thanks to social media platforms, whose witless “who, us?” posture in the face of misinformation and outright lunacy is a civic embarrassment.

More than that, the use of social media as a platform for outright lies about public figures and, in this case, malevolent rumors about a pleasant neighborhood restaurant popular with families is a menace to private lives, peace and prosperity. In response to the firestorm of anonymous death threats and warnings directed at Comet’s owner, James Alefantis, and some of his employees, D.C. police have had to deploy officers to keep an eye on the restaurant.

So what if Mr. Alefantis has never met Ms. Clinton and neither traffics nor abuses children? Social media, a neutral host body for parasitical insanity, have turned their algorithmic gaze upon him. The culprits include Facebook, Twitter, YouTube, Reddit and other platforms that have done too little to safeguard their sites from deception and fraud. (Reddit belatedly shut down a message board devoted to “pizzagate.”)

Like 93 percent of Washingtonians, the restaurateur happened to support Ms. Clinton for president; he has some prominent Democratic friends, past and present. Mr. Alefantis’s name surfaced in leaked email from Mr. Podesta’s account, published by WikiLeaks, in which the two men discussed holding a Clinton fundraiser. As far as anyone knows, there is no more logic than that as to why Mr. Alefantis and his restaurant became targets.

The First Amendment is a bulwark of democracy but provides no protection for defamatory allegations published in knowing disregard for the truth. Mr. Alefantis is more than entitled to sue for defamation and libel, if he can find the purveyors of the garbage heaved his way.

A separate question is whether criminal charges may arise from some of the threats that have been leveled at the restaurant and its owner, online and by phone. Mischief may stray into the province of criminality if it incites violence.