Am I being censored or deplatformed? ;-)

I'll see myself to the corner...

But if a platform wants to be a "common carrier" and not a publisher with all the responsibilities thereof, it doesn't get to make the distinction, so actually in a very real sense, you are entitled to use the platform of anyone who wants to be a common carrier, by definition.

If you send something controversial via USPS, they don't have any liability for it, and only in very exceptional circumstances would it be intercepted in transit. If they were responsible for everything they carried, the postal service would look very, very different. If it's illegal you can be busted at either end but the postal service itself doesn't care.

You're thinking of the first amendment, there is a nuanced difference between that and the general principle of free speech.

I'll assume you happened to not be aware of this, but there are lots of people online who refuse to acknowledge that difference and continue to spout the "entitled to someone else's platform" persuasion meme, which is kind of what this whole discussion is about: power, or altering the course of future events. If one's ideas & principles are sound, disingenuously censoring opposing ideas shouldn't be necessary. I believe many pro-censorship people know this explicitly (but would never speak it out loud) and others "sense" it subconsciously.

Is the difference between the First Amendment and the moral principle of free speech really that nuanced?

It seems to me one has to be thinking strictly in terms of a single country, a single period of human history, a single document in order to conflate the First Amendment with the moral principle of freedom of speech. This is a very narrow view.

It depends if you're trying to win elections or internet arguments, or to ensure a healthy marketplace of diverse ideas exists, because that is the best way we know of to find the best solutions to problems. Twitter, Facebook, YouTube are where modern people "congregate" and get their "information". Cutting someone off of these platforms dramatically lowers the chances that anyone will hear them, that's the entire point of the action. Claims that dismiss this as no problem "because someone else's platform" are not just saying nothing illegal has happened, they are also essentially saying a free marketplace of ideas is not valuable. This is a very new development in western countries, and it's pretty easy to see how far gone most people are already, even on more intelligent forums like this. Partisan politics trump almost everything on certain topics, even one as important as this.