What about the innocent users on the instance? I think there should be a more measured approach to defederation, looking at the bigger picture and what it actually achieves.

Defederating won’t stop them posting it just means you won’t see it. They’ll then be even more effective at spreading their message as they claim they are being silenced.

Many people are proposing a council that any instance would have to be a member of. If they break the rules (eg not moderating the instance) then the council has the power to migrate innocent users.