The beauty of federalisation is that you can have both. But we should be honest - maintaining a community with closed registration processes takes effort, so it's always going to be smaller than open registration. For people unlikely to get punched, most are going to end up in the soup of generally-federated instances, rather than in a more closed-off but safer network.

And since we're not really talking about people called Mark getting punched, but trans people being exposed to transphobia and things like that, there's also an important distinction that is worth remembering: being exposed to hateful statements is horrible, but not as horrible as being punched. So some trans people do end up staying on lemmy.world and that's also OK.