Trump threatens to 'close' down social media platforms

I wonder, at point is Twitter supposed to block the user for constant spread of disinformation on its platform? Or would that violate the user's right to "free speech"? Could the user protect himself by claiming, that he is simply expressing "his own opinion"?

Public figures have it harder when it comes to using the "it's just my opinion" argument.

YOU can claim vaccines are a fake, and that's bad, but won't have harder consequences on you.

A medical doctor can't claim the same thing without losing their position as a medical doctor; they kinda lose a bit of that "it's just my opinion" card as part of the responsibilities they have with society.

Free speech means the government can't come after you for statements. Anyone claiming a company is infringing on their free speech is at best ignorant of, and at worst purposefully misconstruing, the bill of rights. You have no right to post whatever you want on a private company's platform, they can ban you whenever and for whatever reason they want.

In other words, the only reasons for Twitter not ban such a user are 1) business (that he might be driving a substantial amount of traffic); and 2) PR (that banning him would bring much more negative than positive coverage for the company)?