Community block lists or bans are handled at the protocol level (I think this is task that did that), and are pretty simple, in that they just tell a server not to let a particular user comment or post on a particular community. Thats straightforward enough, and as long as the user’s server obeys that, the user doesn’t get to post.

Trying to do something similar for every user becomes much more complex as it requires coordinating each user’s settings to all the relevant servers every time they change. It also leaves open the issue of what happens if a user you’ce blocked simply posts a sibling comment to yours, as you won’t see it, but the rest of the community will.

Personally, I would like to see invite only communities where posts and comments are public (it’s activitypub, so there’s no huding them), but only whitelisted users can post. I know there’s a WomensOnly community here that has a hard time stopping men wading in (I’m guilty if that, I saw an interesting postvand didn’t notice the community name, but the mods were very nice about it). I’m sure they’d like a way of vetting first time posters and commenters.