I do not really get this discussion about censorship. I don't see any censorship here, I see (rather large) companies exercising their contractual freedom in highly centralized environment. I'll admit that these times there is a narrowly defined narrative what is the right thing to say and think and often companies trying to avoid customer unhappiness in form of a shitstorm tend to follow that narrative to please their customer/user base.
But since you are basically unheard/invisible if you're not on Twitter (anymore) it is a form of censorship nonetheless nowadays. It is somehow ironic how many
BTC-enthusiasts actually use Twitter and not something like
mastodon. Decentralization does not only fix the monetary system, it would also fix social networks and energy production etc.. Email for example is decentralized, gmail might kick you, but then you can use hotmail (or go straight to protonmail if you're one of the brighter candles on the cake) or even register your own domain and run it from your living room on a rpi.
If Amazon decides not to deal anymore with Parler, that is fine by me. If Jack Dorsey thinks the orange nutjob is not worth the trouble anymore, that's his decision. People unhappy with that or missing the wisdom of Donnie should vote with their feet/d and use another company for their needs.
What keeps them from running their own infrastructure? Mind you, that was actually the thought behind the internet, being decentralized and everybody being able to run a service on their own computers.
One addition to the above, I might have left the impression that you and I are customers of Twitter or Parler or Facebook, that is not what I meant. We are in fact a supplier, we deliver the product that Facebook sells to advertisers, governments and aliens (basically everbody who pays for it). In turn we are paid for our generous delivery (you'd be astonished what the data about you - your data is worth to them) with "free" services that we can use. This bargain seems obviously too good for most of us to take care and take things into our own hands (i.e. using open standards like
Jabber) and run our own services or use easily exchangeable small service providers that offer that to us for a small fee.