Also: your Mastodon admin could well be someone you know personally, rather than @jack.
Ah, assuming that's true this is the first I'd heard. My guess is that we'll see more of this as a handful of instances dominate and (in at least some cases) consolidate.
My point about @jack is that, for now, you're trading one benevolent dictator for many. The result is a Tower of Babel of moderation and federation standards. Maybe that's a feature and not a bug?
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I run a Mastodon instance and I sure am not blocking counter.social and I sure do not see a single toot from them anywhere in my database. Mr. Actual The Jester followed me for a day or two and then just vanished from federation along with the rest of his instance.
Edit: Damn, that was a stupid comment, but I'll leave it as penance. I just wasn't seeing that Mastodon is perfectly setup for compartmentalization. So my Mirimir persona would have an account on some instance that focused on privacy, security and anonymity. And I would be protected from off-topic trolls. But I could have other unlinked personas on other instances, with different topics and blocking criteria. That's very cool.
You'd think, but no. Some instances are run by "free speech absolutists" (in quotes, because they're really not) who block instances which, in their opinion, are "too aggressive" about blocking spam and bad actors. For example, mastodon.social blocks counter.social, preventing all counter.social users from federating with mastodon.social users.
In other words, Twitter users have to deal with the opaque decision making of one @jack. Mastodon users have to deal with the opaque decision making of a bunch of @jacks.