@utzer !gnusocial Except:
a) When most speech originating from the node is illegal (a neo nazi node spouting holocaust denial propaganda to a German node, or take IamOver18 and a node that's in Saudi Arabia where the mere existence of pornography is highly illegal)…
b) An admin might run a node specifically for a target demographic (let's say kids) and doesn't want NSFW content or hate speech being broadcasted to the node at all.

No, admins and users both need the ability to block users and whole nodes at the very least. Then if somebody wants to get more granular and say "exclude from public timelines" then that's fine, but at the bare minimum users need the ability to block all notices from a node or user from ever appearing in their timeline, and admins need the ability to block notices from a node or user from appearing in everyone's timeline.

I would also suspect that an admin block would effectively ban a node or user from a group that's hosted on a node too. If not, then I think it should.