Sooner or later you will need spam protection and you will subscribe to one of many centralized anti-spam services.

We need centralization at the service of decentralized protocols.

There is no need for a distributed architecture when the users need and ask for partial centralization.

See Mastodon, for example; people who want echo chambers are happy, and those who don't, well, they complain about it but they can't rely on one-by-one muting forever. On nostr they could subscribe to someone's mutelist. Specialized muters (censors) will show up and supply for that demand. Who, for all intents and purposes, would play the same role mastodon admins play.

You are trying to solve the wrong problem here. The problem is not centralization, it's liability.