To be fair, while Lemmy is a step in the right direction, I don’t think it’s aimed quite right. It solves one problem while introducing a host of others. I’ve talked about this previously in various places, but ultimately I think it’s a mistake to bundle communities, user accounts, and moderation all into the same package. It’s easy from the standpoint of “Lemmy is just a mini Reddit” mental model, but then you run into problems like exactly what’s being discussed in this thread, where you have instance administrators making decisions about what federated content their users are allowed to access.

A better design would be to decouple users from communities. Communities should be hosted on super targeted instances with similar communities who all can agree on content rules with each other. That in combination with some kind of central registry of communities and a mechanism to repost content between communities that wish to be partnered with each other would take care of that part of the equation. I would also invert the relationship between user registries and communities. The community should be where the user goes to view content in that community, just with an account provided by a 3rd party, similar to how OpenID worked. The only tricky part is working on how to do a unified front page with content from many communities, as that would imply that all that content would live in one location, and then you run into the legal issues of nobody wanting to allow arbitrary federated content to be rehosted on their server.