That sounds worse than I thought it was. I just assumed Mastodon was like Lemmy, where every instance federates with every other instance basically by default and there’s only some high-profile defed exceptions.
A Fediverse where federations are opt-in instead of opt-out sounds like actual hell. Yeah, more control to instances, hooray, but far less seamless usability for people. The only people you will attract with that model are the ones who think having upwards of seven alts for being in seven different communities isn’t remotely strange or cumbersome. That, and/or self-hosting your own individual instances. Neither of these describe the behavior of the vast majority of Internet users who want to sign up on a platform that just works with one account that can see and interact with everything.
My true hell would be instances only federating explicitly through whitelist. If what the other reply I received about Mastodon is correct, and if Lemmy behaves similary, then they operate on an implicit auto-federation with every other instance. Actual transaction of data needs to be triggered by some user on that instance reaching out to the other instance, but there’s no need for the instances involved to whitelist one another first. They just do it. To stop the transfer, they have to explicitly defed, which effectively makes it an opt-out system.
The root comment I initially replied to made it sound, to me, like Mastodon instances choose not to federate with one another. Obviously they aren’t preemptively banning one another, so, I interpreted that to mean Mastodon instances must whitelist one another to connect. But apparently what they actually meant was, “users of Mastodon instances rarely explore outward”? The instances would auto-federate, but in practice, the “crawlers” (the users) aren’t leaving their bubbles often enough to create a critical mass of interconnectedness across the Fediverse?
The fact we have to have this discussion at all is more proof to my original point regardless. Federation is pure faffery to people who just want a platform that has everything in one place.