Highly problematic.
> We just saw Apple, Google, Facebook, Twitter, and Amazon censor a sitting President
What are you talking about? He's the president. If he has something to say, there are a million ways for him to get the message out.
> But these are actions that ought to be taken by governments
A government compelling a person (or a private company) to publish something is in violation of the law in many countries, often a constitutional law (Example: That violates the first amendment quite clearly, in the USA). I also think most folks would find that highly suspect.
Bigger companies shutting out smaller ones is highly problematic, but then laws do exist to stop this (anti-trust laws). These probably need an update. Whatever update they get, if they prevent Parler's shutdown they went too far. I'm pretty sure that shutdown wasn't about 'eliminating' a competitor at all.