Sebastian Mallaby is the Paul A. Volcker senior fellow for international economics at the Council on Foreign Relations and a contributing columnist for The Post. He is the author of “More Money Than God: Hedge Funds and the Making of a New Elite.”

Until last week, the quintessentially absurd bubble was the Dutch tulip mania. At least the South Sea bubble of the 18th century involved fraud: Investors thought they were buying shares in a valuable company. At least the dot-com bubble of 1999 involved technological promise: Investors thought the Internet would transform business even faster than it has. But in Holland in the 17th century, investors bid the price of simple tulip bulbs up to ridiculous heights. It was the purest of idiotic fantasies.

Last week, a similar fantasy reared its head: the idea that GameStop, an ailing retailer whose shares had slumped from $57 to $4 since 2013, should suddenly trade at $350. The speculators driving this 8,750 percent revaluation have no evidence that this makes sense: Indeed, they disdain evidence. GameStop’s price-to-earnings ratio is infinite, because the company earns nothing. Its prospects are grim, because it is mainly a brick-and-mortar vendor of video games, a product best sold digitally. But the speculators don’t care. They believe. And the force of their belief has been contagious and self-fulfilling.

This is not the worst of it, however. Financial markets are usually stabilized by rational investors: If the crazies drive stocks to an absurd height, thoughtful people take the other side of the trade until prices reconnect with reality. The correction can be late and messy — it’s hard to be thoughtful when markets are wild — but at least our culture generally applauds the partisans of rationality. After the subprime bubble popped, the plucky minority that called out the excess became minor folk heroes. There was even a movie about them.

So far, this time is different. The GameStop speculators are not merely in a frenzy about one stock. Their goal is to destroy the traders who link stock prices to fair value. To suggest a political analogy, they are not just blindly devoted to their candidate; they deny the legitimacy of the opposition party. They are not just acting within the system; they want to overthrow the system. It’s as though — just imagine — a rabble gripped by conspiracy theories were to attack the rules of democracy itself. The name “GameStop” is apt.

Rep. Alexandria Ocasio-Cortez (D-N.Y.) streamed to Twitch once again to discuss the recent GameStop stock phenomenon. (The Washington Post)

The particular targets of the GameStop crowd are hedge funds and short sellers. Here, a couple of definitions may be useful. Generally speaking, a hedge fund is a small-to-medium-size company that makes money by choosing smart investments. There is nothing nefarious about this. To the contrary, if you don’t like too-big-to-fail banks that get backstopped by taxpayers, small-enough-to-fail hedge funds ought to be celebrated. If you worry about complex financial conglomerates with corrupting conflicts of interest, single-purpose investment boutiques are simpler and healthier. On the online forums where the GameStoppers congregate, you read complaints about hedge funds being bailed out during the crisis of 2008. Actually, banks, brokers, insurers, mortgage providers, money market funds and even car companies got rescues. Hedge funds got nothing.

What about short sellers? These are specialists who research stocks that might go down, sometimes because bosses are illegally covering up bad news about their companies. When short sellers identify a case of fraud or similar, they borrow and sell the stock, hoping to buy it back at a lower price later. Again, there is nothing evil about this. To the contrary, it’s a way of keeping prices honest. A market without short sellers is like a political system without investigative journalists.

This, however, is not how GameStoppers see things. They have gone after a short seller named Andrew Left, hacking into his social media accounts, sharing his personal information online, ordering dozens of pizzas to be delivered to his home in the middle of the night, and texting his children with threatening and profane language, according to the Wall Street Journal. Perhaps not surprisingly, Left has announced he will stop playing the game. Irrational stock prices will be that much likelier.

The worry is that the GameStoppers will now target others. Short sellers operate in the open: You can check short-selling volumes for any given stock on Yahoo. By whipping up frenzied buying of a heavily shorted company, speculators can cost the shorts billions and maybe put them out of business. Already, GameStoppers are buying other beaten-down companies, such as cinema giant AMC. A Goldman Sachs index of heavily shorted stocks is up sharply this month because the shorts have been routed.

Hedge funders and short sellers are out to get rich: They are certainly not angels. But there is a difference between trading based on evidence and research and trading based on conspiracy theories and mob tactics. Over the past week, it’s been tempting to celebrate the colorful rebels — they represent the democratization of finance, the revenge against the fat cats. Now it is time to remember that truth matters.

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