Fediverse

That happens whether they are defederated or not. They have 1.6bn users, the rest of the fediverse is a rounding error.

This is what happened with XMPP:

In 2013, Google realised that most XMPP interactions were between Google Talk users anyway. They didn’t care about respecting a protocol they were not 100% in control. So they pulled the plug and announced they would not be federated anymore. ...

As expected, no Google user bated an eye. In fact, none of them realised. At worst, some of their contacts became offline. That was all. But for the XMPP federation, it was like the majority of users suddenly disappeared. Even XMPP die hard fanatics, like your servitor, had to create Google accounts to keep contact with friends. Remember: for them, we were simply offline. It was our fault.

Even if the entire fediverse defederates from the Meta instance, they have a huge network which already exists. And people who want the things that a huge network brings will want to be part of it. Mass defederation will just push some people onto the Meta instance because it's the only place a huge network is operating (and many already have an Insta account so they're already on it anyway).

That's not to say that federating with them is necessarily better. Some users will prefer a smaller network. Some instances will want better moderation than Meta are likely to provide. Moderation issues might make it nigh on impossible for most instances to federate anyway.

But you can't stop them dominating the fediverse by universally defederating. That is not an option. Gmail got big enough to not need XMPP federation; Meta and other potential mega-corp instances are already huge, they don't need us at all.

The best hope might be for several mega-corp instances to hold each other hostage. Google could kill XMPP because none of its users understood that they were part of a federation and barely noticed when the tiny proportion of non-google users disappeared. But if there's a Meta instance and a Google instance and a Mozilla instance ... it's hard for one of them to unilaterally withdraw without handing their users over to a competitor.