[TeMPOraL]

> That's how it is on Reddit too no? You visit and post a comment on subreddit A, somehow mods in subreddit B will find out and pre-emptively ban you.

Almost no one runs a personal instance. Most people have accounts on multi user instances. This is unlike reddit, where accounts are global and independent of subreddits. On reddit, mods from subreddit B can preemptively ban you after they learn that subreddit A doesn't like you. But they can't ban entire subreddit, say C, so that every user that's subscribing to C can no longer interact with anyone subscribed to B. This is the scenario that plagues Mastodon - not individual blocks, but defederating whole instances.