That social welfare perspective is a wider lens that appeals to Mr. Romer and others.

“I’m totally on board with Paul on this,” said Rebecca Henderson, an economist and professor at the Harvard Business School. “We have a much broader problem than one that falls within the confines of current antitrust law.”

Mr. Romer’s specific contribution is a proposal for a progressive tax on digital ads that would apply mainly to the largest internet companies supported by advertising. Its premise is that social networks like Facebook and Google’s YouTube rely on keeping people on their sites as long as possible by targeting them with attention-grabbing ads and content — a business model that inherently amplifies disinformation, hate speech and polarizing political messages.

So that digital ad revenue, Mr. Romer insists, is fair game for taxation. He would like to see the tax nudge the companies away from targeted ads toward a subscription model. But at the least, he said, it would give governments needed tax revenue.

In February, Maryland became the first state to pass legislation that embodies Mr. Romer’s digital ad tax concept. Other states including Connecticut and Indiana are considering similar proposals. Industry groups have filed a court challenge to the Maryland law asserting it is an illegal overreach by the state.

Mr. Romer says the tax is an economic tool with a political goal.

“I really do think the much bigger issue we’re facing is the preservation of democracy,” he said. “This goes way beyond efficiency.”

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