Homeland Security Secretary Alejandro Mayorkas testifies before the House Judiciary Committee in Washington, April 28.

Photo: Evan Vucci/Associated Press

It’s always exciting for progressives when they create a new government office of something or other. They live for this: another excuse to spend piles of taxpayer dollars; another polysyllabic title and flashy logo; another opportunity to extend the long, comforting arm of the bureaucracy into the business of ordinary citizens who never knew how impoverished their lives were without it.

So there was a tangible buzz of excitement around Washington last week when the Department of Homeland Security proudly inaugurated the Disinformation Governance Board.

Other than its title and the identity of its executive director, there’s not much we know about this exciting-sounding new body. Its job, Secretary Alejandro Mayorkas told a congressional committee last week, is to tackle falsehoods that threaten the national security of the U.S. He made it sound over the weekend as though it is all about preventing human traffickers and smugglers from misrepresenting themselves—all harmless enough.

But we also learned last week that it will be headed by Nina Jankowicz. Her Twitter feed makes her look like a cross between Madame Mao and Bette Midler—a mix of impeccably conformist left-wing views about politics and media misinformation—the Hunter Biden story was Russian disinformation, the Steele Dossier was all true, etc.—with excruciating political parodies of musical-theater numbers. Watching her videos is a little like being an audience member at a Christmas concert in a prisoner-of-war camp.

The institution she heads—let’s call it the DGB, which has a nice ring to it and is close enough alphabetically and in spirit to another three-initialed organization from another country that was tasked with enforcing the official version of the truth—is potentially a vehicle for all kinds of new rules to stop the left’s version of untruths emanating from media and tech firms.

But how might it work? Will it have investigative powers? Will it be given its own enforcement resources? Is it going to solicit referrals from the public? Will operators be available around the clock to answer calls from concerned neighbors about violations of information protocols?

“Hello? Is that the DGB? I think the people next door are watching Fox News again.”

Ms. Jankowicz and her little corner of the proliferating bureaucracy sound so preposterous that they’re easy targets to mock. Mr. Mayorkas tried to clean up some of the mess, insisting free speech was safe.

But our progressive overlords are on the warpath against what they define as misinformation and disinformation, and it’s no laughing matter. You can see it in their hysterical reaction to Elon Musk’s planned acquisition of Twitter.

When the site banned various accounts and people on the right it was, we were told, simply a private company, with no special public obligations. Now the prospect of a wider range of voices on the platform is a dagger aimed at the heart of democracy and must be regulated.

“People are dying because of misinformation,” Barack Obama told a Silicon Valley audience last month. You may remember Mr. Obama. He’s been a tireless warrior for years in the twilight struggle for truth in politics. If you have a long enough memory you’ll recall that he was the president who gave a speech in 2009 to promote his signature healthcare measure, in which he attacked critics of the plan for their “scare tactics and fear-mongering.”

Summoning his famous oratorical skills at a crucial moment, he was as determined then as he is now to lay to rest all the misinformation his opponents were peddling: “No matter how we reform health care, we will keep this promise: If you like your doctor, you will be able to keep your doctor. Period.”

We don’t know how many people died because of that piece of misinformation—a whopper of such proportions that even PolitiFact, the self-appointed arbiter of truth and lies, awarded it its coveted “Lie of the Year” title in 2013—five years after rating it “true”—by which time it had become clear that what critics had been saying about ObamaCare was in fact neither scare tactics nor fear-mongering but the truth.

It was certainly a consequential falsehood—one that in 2009-10 helped shore up what little popular support there was for ObamaCare and perhaps persuaded some doubtful Democrats to vote for it.

Yet, even as it was exposed, no one, as far as I recall, was saying the president should be prohibited from contributing to national discussions on a major tech platform.

You don’t promote truth by banning error. You don’t have a monopoly on truth in the first place, and you may discover your “truths” are errors or lies. Even if you’re right, and epistemically 100% certain, it doesn’t give you the authority to ban someone from saying something different.

The only proven effective way to counter bad information is with good information. The only way to overcome lies is with truth.