I prefer sanitized spaces too. I just want to have a sanitizing tool in my own hands - sanitizing what I personally read. But my tool should have no influence on what you will see and read.

Moderation is probably needed. But it should be decentralized.

Decentralized moderation is a fantasy. Do you want to clean every public bathroom before you enter it ? Uncover every troll personally on Twitter every time you log on?

Malign activity (bots and trolls) are organized and at scale, the only way to fight back is at the same scale. Individual users would be helpless.

Not if they were given the same power i.e. moderation tools that Twitter et al have behind the scenes.

Why can't I, for example, set a filter that removes bots based on some confidence value? Or that orders my feeds in the order of my choosing?

Right now I have to use ridiculously blunt instruments and trust in moderation that is well known to be biased and, frankly, useless.

Fair points, but I would argue you aren't describing decentralized moderation so much as centralized moderation tools being made available to users in a transparent way. Which sounds good to me.