The fediverse being decentralized means that there are many servers/instances, each with their own codes of conduct (or lack of one). Similarly, different communities on those servers can have different rules they might want to enforce with removals of posts or comments. For example, a community about cat pictures will have a rule about posts having to be cat pictures and will remove a post about your grandma's vegetable soup recipe.

If your comment/post was removed, that probably means your post/comment was either against the rules of the community or against the code of conduct of the entire server/instance. If it's the former, look for or create a community where that kind of content is appreciated. If you're running up against the code of conduct of the instance, look for a server/instance where your content wouldn't be violating the code of content or make your own server/instance where you're the one defining the code of conduct. Of course, that code of conduct would only apply to communities on your server.

If your server becomes a source of constant shit, admins of other servers might decide to defederate from your server. Think of it like making your own email server: if too many of your email server's emails are spam, other email providers might decide to designate your email server as a spam factory and block all emails coming from it.

Centralisation in this instance refers to control over the network and standard itself rather than control over what's posted on it. There's no single authority that can unilaterally change how every Fediverse instance and system works - for example, there isn't anyone who can decree that from now on Lemmy will no longer allow connections from Canada, or that nobody is allowed to post pictures of capybaras any more.

It's intended to prevent a /u/spez or Elon Musk situation where one asshole can bring down the entire ecosystem built around an API. Nothing stops anyone else from hosting their own instance if they dislike lemmy.world, whereas if you don't like Twitter, you can't just host your own copy of it.

Monero.town is very lax when it comes to moderation as long as you don't say anything that could get you arrested in Germany.