Yes and we're private citizens who can criticize it all we want for banning people we like. So the world turns.

Yes.

What a shame there aren't more decentralised services like email, the web and Usenet (which is now pretty much dead).

Twitter can do pretty much what it wants to who it wants, and they don't have to give a reason.

Maybe you get banned due to an algorithm mistake. Or an individual contracted by Twitter who doesn't like what you said. Or maybe they misunderstand what you said due to cultural differences.

I found my time on Twitter was fighting against a US-biased culture, and what I consider friendly banter with friends can be misconstrued as abuse by some random moderator or algorithm.

Yes and? Sci-Hub is a resource whose value transcends American IP orthodoxy and their contributions to Twitter are a gain for humanity. If Twitter can platform totalitarian governments that commit crimes against humanity why not a mere IP violator?

Yup. Private citizens and organizations can do many shameful, reprehensible things, such as engaging in arbitrary (and legal) censorship, such as what Twitter does.

Only assholes decide unilaterally for other adults what they're allowed to see and read.

Sure, but once a platform is read by billions of people and is influencing what they think, I believe it is reasonable that people discuss about the opportunity to regulate this kind of stuff.