Although we think of HN as a community, we still tend to deal with it in terms of the shared domain objects we create here—links, comments, and votes. We ignore that there are people sitting around this table and playing with the shared collection of LEGO we call a site. If someone keeps building things no one likes, look up from the table and tell the person; don't just take apart the blocks. If we actually want a community, then people should feel social, not just technical consequences for doing things that negatively affect that community.
HN doesn't actually have a good method of going about this, though. Perhaps there should be a user-flagging mechanism (let's call it "intervention") that gives people a chance to air their complaints, in private, to the person, and prevents the person from posting publically again until they've replied to the greviances? There's nothing technical standing in their way of just replying "asdfghjkl;'" and going back to posting, but the social guilt of doing so might make HN feel "real" enough to discourage it. Plus, we could stick a "review user" link beside those replies, so people that felt they hadn't been given adequate response could submit the person to the mods for a possible ban.