Of course, Farley and Friedman have a financial stake in the health of the exchanges. But there is a broader logic to their professed concerns. Traditionally, promising young companies turned to the public markets to raise capital in order to expand their operations; this gave individual investors a shot at owning a piece of those companies’ hoped-for success, either by buying their stocks directly or, more commonly, by holding them in a mutual fund or index fund. Today, more and more start-up companies secure funding from private investors, cutting most Americans out of the equation.

Robert J. Jackson Jr., a commissioner of the Securities and Exchange Commission who previously worked at Bear Stearns underwriting IPOs, told me there can be real distributive consequences when the highest-growth companies are private. If many of the economy’s greatest success stories aren’t included in the funds that ordinary Americans hold, only the wealthiest members of society will enjoy the gains, intensifying inequality. “It’s a good enough argument for me to care about wanting more companies to be public,” Jackson said. SEC Chair Jay Clayton agrees. In his first major speech, he warned: “The potential lasting effects of such an outcome to the economy and society are, in two words, not good.”

The initial public offering was once the ultimate marker of start-up success. Founders of a company might get their idea off the ground by asking family members and friends for seed money, then turn to angel funders, venture capitalists, and private-equity investors to keep the lights on during the fledgling years. But the goal was typically an IPO. Historically, private investors have been willing to risk only relatively small amounts with any one company, and they have tended to exit any investment within a few years. The IPO gave a thriving company a base of capital and announced to the world that it had arrived. Throughout the 20th century, one of the most revered symbols of a mature business was the framed ceremonial gavel its managers had used to ring the New York Stock Exchange bell.

An IPO is still the best means for many companies to obtain liquidity; selling shares on a public exchange remains easier and cheaper than in the private markets. But staying private has, for a variety of reasons, become more alluring than it used to be.

Going public is expensive. Investment bankers, lawyers, and auditors collectively charge millions of dollars to prepare the lengthy registration statement that must be filed with the SEC before shares can be sold. And that’s just the beginning. It costs millions more to comply with ongoing-disclosure requirements. Public companies also incur the harder-to-quantify costs of opening their books to the scrutiny of securities analysts, activist investors, the media, and short sellers. Equitable Financial, a Nebraska bank operator that delisted from Nasdaq this summer, said it was doing so in order “to eliminate the administrative and annual fees associated with being listed on Nasdaq.”