By WWI, the cost in today's dollars for a newspaper grew to several million. People can't live off small papers today. They live off Patreon and YouTube. They depend on distribution platforms in a way we didn't before.
If Amazon bans your books, it's effective censorship for people who only read eBooks. Sure you can distribute the epub/mobi DRM free, but few people are going to bother with that (or know what to do with the file).
I've written about this before:
https://fightthefuture.org/article/the-new-era-of-corporate-...
If Amazon bans your books, you can still buy the book elsewhere, or get it from the author's site. Just because a piece of information isn't in the medium that you prefer to consume doesn't make it "censorship." It's not on Amazon that "few people are going to bother with that" when they ban you for violating their ToS.
A truly libertarian Internet would still have the first issue, because of freedom of contract. But it wouldn't have the second, because having an IP address reachable from anywhere on the Internet and hosting any content you chose would be a basic right. (One could argue that having a DNS routable name for your IP address should be part of that right too, but the absolute requirement is the IP address: anyone can reach you with that even if there is no domain name corresponding to it.)
All of this seems to be something along the lines of "it's inconvenient, so it's bad, and [they] shouldn't be allowed to make it inconvenient on _their_ platform".