I want to be clear I am not advocating de-federating from mastodon.social today. I used de-federation as an example to underline the problem related to the size of m.s.
And as many people have noted in replies to this thread, there are many other tools at admins'/mods' disposal, like silencing an instance.
Defederation is a nuclear option and should only ever be used as an absolutely last-resort.