American law and culture strongly circumscribe government power to regulate speech on the internet and elsewhere. Regulations of social media companies might either indirectly restrict individual speech or directly limit a right to curate an internet platform. The First Amendment offers strong protections against such restrictions. Congress has offered additional protections to tech companies by freeing them from most intermediary liability for speech that appears on their platforms. The U.S. Supreme Court has decided that private companies in general are not bound by the First Amendment.
However, some activists support new efforts by the government to regulate social media. Although some platforms are large and dominant, their market power can disintegrate, and alternatives are available for speakers excluded from a platform. The history of broadcast regulation shows that government regulation tends to support rather than mitigate monopolies.
I think that this gets it mostly right.
My worry is that American culture no longer supports free speech. We can make exceptions for speech that causes direct harm, such as shouting “Fire!” in a crowded theater where there is no fire. But hurting someone’s feelings should not count as direct harm. Racist remarks or Holocaust denial may be uncouth, but in a culture of free speech they should be permitted.