So your solution to people using a decentralized, federated protocol to say things you don't like is to stop various servers interacting with each other? At that point why not just use federated services with multiple accounts?
It seems far too risky to sign up on a service for the purpose of intercommunication that is able (or even likely) to burn bridges with another for any reason at any time. In the end people will just accumulate on 2 or 3 big providers and then you have pseudo-federation anyway.
My solution is for instances to stop being negligent. Mastodon still directs everyone to create an account on mastodon.social using dark patterns (see https://joinmastodon.org/), which has lead to the flagship instance being far bigger than its moderation team can handle, leading to a situation where it's a major source of abuse and where defederation is too costly for many to consider.
"People will just accumulate on 2 or 3 big providers" is far from an inevitable circumstance, but there are conditions that make it more likely. That, too, is largely down to negligence or malice (but less so than the abusive communications problem).
Servers stopping federation with each other is pretty normal IMO. If I had a mastodon server I would also not federate with something like gab.com.
However all the LGBT+ friendly servers federate with each other and that's good enough for me. I like not having to see toxicity, there's too much of it in the world already.