When they removed XMPP, they disconnected the Google users from the rest of XMPP. And since it was the largest instance, XMPP as a whole basically died. People couldn’t use XMPP to stay in touch anymore with people using Google’s thing, and vice-versa, which XMPP as a whole kind of came to rely on.

And how is this different from not using XMPP (or being defederated) in the first place? Their platform would still have become huge and pulled over users. People don't use a platform because they like the technology. They use it because it has people they want to talk to. Even google themselves had to accept that with their failed Google Wave which didn't even survive the closed beta because people who got an invite couldn't talk to their friends who didn't get one.

And I'm explicitly not assuming Facebook will play by the rules in the long run. I'm saying while they do, let's talk to them, even if it's just for a month. When they eventually start breaking the rules, we can still defederate and I assure you that we won't lose significantly more users than we would have if we had defederated earlier. Because why would we? We're on the side of the open-closed divide that values privacy and open source software. Our only reason to ever switch to Threads is to talk to people that aren't on Mastodon/Lemmy/Whatever. If that's a requirement for someone they have to do that either way. But for someone who starts out on Threads, we might suddenly create an incentive to create a Mastodon account to keep talking to their friends. They probably won't leave Threads but they will use both, pulling the fediverse into the public conciousnes.