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.