This is what I was wondering.

There are ways to do it. Whitelists and blocklists people can subscribe to (with different moderation strategies), with maybe default logic for integrating different lists and an easily extensible format for clients or end users to write their own scripts to do more complex combinations would go a long way.

But as much as "decentralized" sounds cool, I think more structured communities for content work better. Reddit worked so well as a source for information before it shit the bed because it allowed communities to form with their own standards and ideas. It was flawed, but a hell of a lot more coherent than twitter was, because structure is useful.