> unless the platform is run by the government. The First Amendment applies to restrictions on free speech by the government, and is not related to the actions of private enterprises.
That's not quite accurate. There is precedence for regulating speech in private media for example, as in the case of broadcast networks. Broadcast TV networks are still restricted on speech/expression to this day, as are radio stations.
There's nothing to say that social networks can't also be brought under the regulation of the FCC and have their speech and terms of service dictated to them. This turns social media platforms into something more like a utility. All users must be treated equally or the platforms get massive fines. If I were attempting to get this through, I'd argue the major social media platforms are natural monopolies due to reinforcing network effects and the finite nature of user time (there can only reasonably be so many large social networks, and the market has already strongly demonstrated globally that that is a very small number). You can replace a natural monopoly with another (an independent Instagram, allowed to evolve as a threat, possibly could have killed Facebook for example and become the new monopoly), but you can't have 100 Facebooks that will all perfectly compete with eachother (some people will argue that in theory you could, but that would never happen in reality). For whatever niche / category / concept they target, social networks inherently trend toward either consolidation of users or death; it's why the Twitter clones were all killed off in the early days when people were still experimenting with that social concept. It's why there are not dozens of large scale YouTube or Reddit or even Stackoverflow clones (the rather brutal combination of network effects and finite user time wins in all cases and you end up with consolidation of users to just a few viable platforms). The market, largely left to sort things out on its own in the social media sphere, has provided a lot of proof that large social media platforms are natural monopolies.