Yeah, I'm not disagreeing there is a convenience and ease angle, but I think there's a middle ground where we have 2-3 communities for major interests with somewhat different vibes or approaches, so there is a topic reason for them coexisting. This already happens in the old school forums ecosystem. Fediverse's advantage here is that you hopefully don't need separate accounts.

Re: loss of knowledge, if some instance/community does a purge, I'm assuming the old posts are still there, at the very least on the instances that used to be federated with them. I suppose it would be a nice to have a feature for admins for "freezing" their public backups of mirrored communities when they get defederated. It's not that different of a scenario from standard Internet drama, we just have to handle this nicely.

I agree with other people that the right to defederate is to be respected. If we rely on one hub community somewhere to congregate, this is only kinda decentralization. At the very least the central hubs shouldn't be on instances that are too defederation-happy.

On the other hand, I see the argument that many users means more difficult moderation, where defederation might be a band-aid as they say on beehaw. The question is if they have too ambitious moderation goals to handle being a central hub, and maybe indeed it would be better for their communities to be sort of internal to them.