So in terms of beehaw vs lemmy.world I would be on instance 3 - I can see and participate both, their defederation from each other doesn't affect you, it only affects the users of beehaw or Lemmy.world
This aspect is really crucial for people to understand, so I wanted to emphasize it. This is what gives the Fediverse it's hyper free nature, where if you don't like which instances your instance has chosen tp block, you can always switch to a third instance and have access to both your old instance (thus solving the network effect) and the new one (thus giving you freedom of association). This sort of connected-by-default design choice (I.e. using blacklists instead of whitelists) is also crucial for maintaining the general interconnectivity of the network thats crucial to its functioning.
We need to crowd source a common list of instances to block from users and mods across the network for instances to use, like people on Mastodon started doing. It was really effective. Defederation is really the only way to deal with / only check on users that sign up on instances that don't moderate them at all in order to harass others with impunity, since moderators can't effect users on s different instance and so it basically gives such users free reign. That's why IMHO defederation is a REALLY crucial tool to make this place livable, otherwise it'd be filled with trolls doing their thing with absolute impunity and there would be nothing mods, who are supposed to be the first line of defense for that kind of thing, could do,