I don’t think instance level blocks should be overridden. Some blocks are the result of moderation disagreements (beehaw vs lemmy.world vs exploding-heads vs hexbear), others are because of NSFW content, but there are a bunch of Fediverse servers full of pornography that would be illegal to host in many countries around the world (lolicon porn, for instance). If an administrator doesn’t want that trash on their server, they should have the ability to block it.
I think there’s a significant difference between completely blocking off a remote instance and making all interactions with said instance opt-in, and the server administrator should always have the final word. I think leaving the moderation on a separate layer like Nostr and Bluesky do it (not that Bluesky is federating at the moment) was a mistake, the result of some laudable free speech ideals that just don’t work out in the real world.