Overall:
If it serves the explicit and implicit goals of HN, I don't find issue with hellbanning.
Especially since I think pg doesn't particularly care about most people's opinion on this (nor should he)
I guess my counter argument would be that it's a problem when meta on a different thread, or when there are more than 1 or 2 meta threads a week. Otherwise they are easy to avoid and infrequent enough that meta threads don't crowd out more legitimate ones.
It's a very useful technique for fighting spam and trolls because it hides their activity from the rest of the site, yet they don't know that there is a problem so they don't work around it or create a new account.
The HN mods like to use hellbans on trolls, however it can sometimes be hard to distinguish a troll from a misguided or obnoxious user. Also, sometimes an otherwise good user will have a thread where they come off as trolling for one reason or another. In these cases it can be hard to know whether a user should be banned or not.