I honestly wish that the answer is "when we get so big to the point that a single machine can not handle it, we close registrations".
Can we please drop the "number must go up" mentality? The whole point of federated systems is to avoid concentration of power in a handful of servers. I'm sure that the people doing there have good intentions, but why can't we just let things just a little bit dispersed?
Sure, until you google some error, or some other random thing, find some thread somewhere, want to comment/ask/contribute, and you can't, since the registrations are locked.
I'm on kbin.social and participate in communities across ~20ish other instances regardless of whether they've turned off registrations temporarily or permanently. Disabling registrations only prevents new accounts on that instance, it doesn't stop people from posting and commenting from other instances.
Parent comment is the perfect example of how we got so used with dealing with shitty and user-hostile systems. We've been dealing with walled gardens for almost a generation now, it's like they don't even understand that it is possible to interact with a remote system without having everything in one centralized database.
I think what the parent is alluding to, is the fact that, Googling something and ending up on a Lemmy instance that is not your local one. You can, in fact, not comment on these instances. You must access it through your local instance (e.g. lemmy.world/c/community@remote.com).
A browser extension? While I agree, the client (browser) probably has to know about ActivityPub, or store some state that sites can read (without third party cookies), it's not fair to expect users install a browser extension for what would be basic functionality in their eyes.
Can we please drop the "number must go up" mentality? The whole point of federated systems is to avoid concentration of power in a handful of servers. I'm sure that the people doing there have good intentions, but why can't we just let things just a little bit dispersed?