Two billionaires now control the four biggest global social media platforms, the “de facto public town square … [and] bedrock of our democracy ”, in Elon Musk’s words.

Musk’s purchase of Twitter, with its 300 million daily users, still requires regulatory approval but it puts him alongside Mark Zuckerberg who controls Facebook’s more than one billion users, as well as those of Whatsapp and Instagram.

Musk’s leveraged buyout of Twitter will mean he is constrained only by a considerable debt burden that presumably will require him to raise profit-levels. Zuckerberg has a pyramid share structure that ensures him and his heirs full and eternal control. They operate in a barely regulated industry, though the European Community is moving to introduce some rules and regulations.

It can’t be healthy for two men to wield such unconstrained global power and to hold the keys to the sustainability of our democracies, especially at a time when many of these democracies are looking vulnerable. These platforms need to be treated as public utilities, serving public purposes, and not only as vehicles for personal power and profit.

The prioritisation of massive profits over public service, and the lack of regulation, has driven Zuckerberg to design an algorithm that is concerned primarily with ensnaring users, even at the cost of causing social damage. As the Facebook whistleblower Frances Haugen said, Facebook promotes hate speech, damages democracy and is “tearing our societies apart” because profit is more important to them than the safety of their users. Haugen revealed that Facebook had ignored research that showed Instagram’s impact on teenage mental health.

There is a long history of plutocrats buying media to stimy criticism or boost their social and political influence We have seen how Rupert Murdoch has allowed some of his outlets to corrupt public debate, spread disinformation and undermine democracy. His power over newspapers and television is nothing compared to the scope and influence of the social media giants.

Musk is a quirky tweeter, using his 82-million followers to promote his business interests and tackle his critics, including the Securities Exchange Commission. Now he will have a free hand.

Musk also has interests which can conflict with a free speech position. What will he do when China – where he has a Tesla plant –  asks him to silence dissenters or suppress inconvenient bits of history like Tiananmen Square?

Musk has said his main motivation is to promote free speech. He has promised to reduce content moderation, open up Twitter’s algorithm and get rid of the Twitterbots that plague the platform.

These aims are welcome, but he seems oblivious to the 10-year battle these platforms have had to clean themselves up, control the vile material that can quickly flood them, and stop hostile forces, like Vladimir Putin, from using them to undermine democracies.

All the social media outlets started out with a commitment to maximise free speech, but found – as does any internet outlet that allows free public discussion – that they were quickly taken over by the purveyors of pornography, hate speech, trolling, harassment and threats. Without intervention of some sort, the public discussion becomes polluted and even dangerous, and this alienates audiences and advertisers.

Making the algorithm open source is a positive development for transparency, but the main benefactors will be those who want to use this access malignly, including foreign interests that want to mess with our public space.

There is a contradiction between Musk wanting to promote free speech and make the platform “trustworthy”. It is possible that as a powerful white man, Musk is less aware of the harassment and trolling that some face more than others, but it is something he is going to have to deal with..

Twitter has been better than Facebook in searching for ways to manage this and still be fair, consistent and favour free speech. Still, they tend to treat celebrities differently from ordinary people, and non-Western countries differently from their own.

It is not easy. They have to apply different laws, cultures, norms and practices in every country they operate. They have to differentiate between genuinely dangerous hate speech and that which is merely disagreeable or discomfiting. They are under pressure from all sides of the political spectrum to be tougher on their opponents and lighter on themselves, so consistency is crucial. And the volume of material they have to deal with is overwhelming. They employ automation and thousands of people to filter material, but it is never enough, particularly as many of these decisions require human judgement.

So promoting free speech is a challenge, especially when you are under financial and political pressure.

It is rocket science, but then Musk is a rocket scientist. I suspect, though, that he is going to find it easier to deal with flights to Mars than the real people of Twitter.

*Harber is director of the Campaign for Free Expression and Caxton Professor of Journalism at Wits U.