I have two thoughts about Twitter's decision, which reflects broader conclusions I've come to about the large internet platforms. On the one hand, I am glad that the company de-platformed President Trump, because there was an active threat to the US government that he was abetting in real time. On the other hand, the ban demonstrated just how powerful Twitter had become: they have taken away the primary channel by which the president of the United States has been able communicate with the outside world, that cannot be easily replicated. I do not think it is legitimate in the long run for a private company to exercise this kind of influence. Twitter's decision was protected by the First Amendment, but the truth of the matter is that it, along with Facebook and Google, have become de facto custodians of public discourse not just in the US but for many countries around the world.
The problem that these platforms pose is one of scale. We have plenty of private companies that curate the information they provide to the public; they're called media companies with names like The New York Times or the Wall Street Journal. But they are still operating in a relatively decentralized and competitive market, and no single legacy media company has the power on its own to, say, throw an election. This is not true of the large platforms, whose role is more like that of the three large television networks in the 1950s and 60s. Back then the US found it legitimate to regulate the way they covered political events, through licensing and the FCC's Fairness Doctrine. It would be appropriate to regulate the internet platforms in a similar manner because they occupy a similarly oligopolistic position, but unfortunately the country is much too polarized today to be able to agree on what constitutes "fair and balanced" coverage. So we need another solution to this problem other than relying on self-regulation and the good intentions of the individuals who control these companies.