The only reason Threads has 30 million users right off the bat is because they leveraged their monopoly position with Instagram to push their users to Threads. It is absolutely no different from how Microsoft leveraged their monopoly position with Windows to push their users to Internet Explorer in the 90s.
Facebook has a long history of buying out any firm which poses the threat of competition. Peter Theil, the literal fucking vampire who sits on their board, has made very blunt remarks about this. They bought out Instagram and WhatsApp for this very reason. Make no mistake. To Facebook, the Fediverse is competition. Every minute spent on Lemmy, Mastodon, PixelFed, and other AGPL federated platforms is a minute lost from the commercial attention economy. Every user who makes the switch is a user which isn’t feeding them a steady stream of marketing data. Every user who makes the switch is lost ad revenue.
Facebook cannot buy the Fediverse the same way they bought Instagram. Instead, they will join it and apply incredible pressure to influence it in directions which are not harmful to their bottom line, and once the threat is neutralized, they will drop it like a hot turd. It could’t be any more obvious what their intentions are, but a lot of the tech bro dipshits still think a “wait and see” approach is warranted, including Eugen (initial creator of Mastodon) himself.
This guy made a blog post this morning saying that Mastodon is different from XMPP. XMPP was only used by a bunch of nerds and that’s why it died. It had nothing to do with Google employing the classic “Embrace, Extend, Extinguish” strategy. Meanwhile like 75% of people on Mastodon have their fucking Linux distro in their bio (gentoo gang, btw).
We might have gotten lucky with a handful of these “Benevolent Dictators For Life,” but only WE can create a network which is liberating and empowering. Nobody is going to deliver it for us.
Federation is managed at an instance level, by the administrators of that instance. Instances can take either an accept-list approach or a block-list approach. As an end user, you choose to de-federate from it by choosing an instance which de-federates from it (or by running your own instance). The moderation / personal block tools on Lemmy aren’t as sophisticated right now as they are on Mastodon, but ideally you should also be able to personally block instances from accessing your account as well.
A lot of third party communication occurs on the Fediverse though. If a community is hosted on server A, you come from server B, and another user comes from server C, it is reasonable to ask if server A will just hand server B’s content (replies, votes, etc.) to server C. On Mastodon, this is the default behavior, unless an instance enables the “Authorized Fetch” option. I am not sure how this works on Lemmy.
For the meantime though, Threads is focused on the microblogging format of social media, and compatibility with Mastodon in particular. Lemmy is probably less at risk. But you should still treat every public post like it is truly public. People run scrapers. People run bots. People can take snapshots on archive.org. Federated platforms are no different in this regard.