AS THIS newspaper went to press, Facebook was about to become a public company. It will be one of the biggest stockmarket flotations ever: the social-networking giant expects investors to value it at $100 billion or so. The news raises several questions, from “Is it worth that much?” to “What will it do next?” But the most intriguing question is what Facebook's flotation tells us about the state of the public company itself.

At first glance, all is well. The public company was invented in the mid-19th century to provide the giants of the industrial age with capital. That Facebook is joining Microsoft and Google on the stockmarket suggests that public listings are performing the same miracle for the internet age. Not every 19th-century invention has weathered so well.

But look closer and the picture changes (see article). Mark Zuckerberg, Facebook's young founder, resisted going public for as long as he could, not least because so many heads of listed companies advised him to. He is taking the plunge only because American law requires any firm with more than a certain number of shareholders to publish quarterly accounts just as if it were listed. Like Google before it, Facebook has structured itself more like a private firm than a public one: Mr Zuckerberg will keep most of the voting rights, for example.

The number of public companies has fallen dramatically over the past decade—by 38% in America since 1997 and 48% in Britain. The number of initial public offerings (IPOs) in America has declined from an average of 311 a year in 1980-2000 to 99 a year in 2001-11. Small companies, those with annual sales of less than $50m before their IPOs—have been hardest hit. In 1980-2000 an average of 165 small companies undertook IPOs in America each year. In 2001-09 that number fell to 30. Facebook will probably give the IPO market a temporary boost—several other companies are queuing up to follow its lead—but they will do little to offset the long-term decline.

Companies are like jets; the elite go private

Mr Zuckerberg will be joining a troubled club. The burden of regulation has grown heavier for public companies since the collapse of Enron in 2001. Corporate chiefs complain that the combination of fussy regulators and demanding money managers makes it impossible to focus on long-term growth. Shareholders are also angry. Their interests seldom seem to be properly aligned at public companies with those of the managers, who often waste squillions on empire-building and sumptuous perks. Shareholders are typically too dispersed to monitor the men on the spot. Attempts to solve the problem by giving managers shares have largely failed.

At the same time, alternative corporate forms are flourishing. Once “going public” was every CEO's dream; now it is perfectly respectable to “go private”, like Burger King, Boots and countless other famous names. State-run enterprises have recovered from the wreck of communism and now include the world's biggest mobile-phone company (China Mobile), its most successful port operator (Dubai World), its fastest-growing big airline (Emirates) and its 13 biggest oil companies.

No doubt the sluggish public equity markets have played a role in this. But these alternative corporate forms have addressed some of the structural weaknesses that once held them back. Access to capital? Private-equity firms, helped by tax breaks, and venture capitalists both have cash to spare, and there are private markets such as SecondMarket (where $1 billion-worth of shares has changed hands since 2008). Limited liability? Partners need no longer be fully liable, and firms can have as many partners as they want. Professional managers? Family firms employ them by the HBS-load and state-owned ones are no longer just sinecures for the well-connected.

Make capitalism popular again

Does all this matter? The increase in the number of corporate forms is a good thing: a varied ecosystem is more robust. But there are reasons to worry about the decline of an organisation that has spread prosperity for 150 years.

First, public companies have been central to innovation and job creation. One reason why entrepreneurs work so hard, and why venture capitalists place so many risky bets, is because they hope to make a fortune by going public. IPOs provide young firms with cash to hire new hands and disrupt established markets. The alternative is to sell themselves to established firms—hardly a recipe for creative destruction. Imagine if the fledgling Apple and Google had been bought by IBM.

Second, public companies let in daylight. They have to publish quarterly reports, hold shareholder meetings (which have grown acrimonious of late), deal with analysts and generally conduct themselves in an open manner. By contrast, private companies and family firms operate in a fog of secrecy.

Third, public companies give ordinary people a chance to invest directly in capitalism's most important wealth-creating machines. The 20th century saw shareholding broadened, as state firms were privatised and mutual funds proliferated. But today popular capitalism is in retreat. Fewer IPOs mean fewer chances for ordinary people to put their money into a future Google. The rise of private equity and the spread of private markets are returning power to a club of privileged investors.

All this argues for a change in thinking—especially among the politicians who have heaped regulations onto Western public companies, blithely assuming that businessfolk have no choice but to go public in the long run. Many firms now go (or stay) private to avoid red tape. The result is that ever more business is conducted in the dark, with rich insiders playing a more powerful role.

Public companies built the railroads of the 19th century. They filled the world with cars and televisions and computers. They brought transparency to business life and opportunities to small investors. Because public companies sell shares to the unsophisticated, policymakers are right to regulate them more tightly than other forms of corporate organisation. But not so tightly that entrepreneurs start to dread the prospect of a public listing. The public company has long been the locomotive of capitalism. Governments should not derail it.