Fair, but in this case we're talking about a US company hosting another US company's data, so I think talking about free speech in the context of the First Amendment is reasonable.

It's not unreasonable, but I think it's incomplete. We may be headed towards a world in which private companies exert a great deal of control over what an individual can say. Not only by controlling communication platforms, but also by withholding employment from people who say certain things.

I don't want to join the argument about whether that's good or bad, but I think it's a huge mistake to simply say "It's consistent with the 1st amendment, therefore it's OK." If we're going to let private corporations use their market power to police individual speech, we need to have a real debate about what that means.

The distinction between private and public sphere is not completely clear.

Let us say that a politician calls Mark Zuckerberg and asks him nicely to squish certain people, and MZ complies. Is that a First Amendment issue or not?

Or, let us say that a politician calls Mark Zuckerberg and offers him some concrete support (in an anti-trust case or taxation matters) for squishing certain people, and MZ takes up the offer. Is that a First Amendment issue or not?

The trouble with both scenarios is that they are certainly possible and hard to prove or disprove. That is one of the reasons why concentration of power in a few hands (even private ones) may translate into bad politics.

I agree with everything you say, but I don't see that "free speech" needs to be the hammer you use to drive in that nail. Concentration of power in the few is bad for many many reasons independent of free speech.

When the government is threatening regulation against the private-sector because these companies don't censor, then I think this could potentially be considered a 1st amendment issue.