Hackers News has the same thing, called hellbanning.
It's a valid mechanism for outright spam, but seems to get overused as sites get more mature. I think you should basically never hellban anyone who has ever done anything even marginally useful on your site. Either talk to such miscreants or explicitly ban them so they know what you did.
[1] It was a meta post. JoS didn't allow meta posts. But it was hard to know this because.. it's a meta rule. And you could keep posting meta posts in ignorance and never get feedback that this was undesired behavior.
It's a matter of ratio. Is their marginally useful contribution worth the hassle that they cause?
Rooting a troll out of something like HN, or Reddit, or a forum is hard. They probably have more time than you.
You said elsewhere in this thread that shadowbanning is required because otherwise they just create a new account. But the new account starts with none of the positive karma the old one did, so it is hellbanned in the usual way.
Literally all this takes is that the site support non-deceptive versions of ignore/kill/nuke/blast and use them the first few times. If the guy sees his stories being flagged and continues, then stop showing him that his stories are flagged.
Also, addlepate, you've been hellbanned:
addlepate 8 days ago | link [dead]
Are you sure about all that? I never get votes or replies. Also, as implemented,
HN's hellbanning is quite obvious when it happens.