This is notably the first time I've found myself disagreeing with you, in many kilocomments over the past several years.
I once thought it was completely terrible, but changed my mind after the losethos guy showed up — secret hellbanning is a great tactic against active trolls, whether they're intentional or clueless.
Unfortunately it and individual deletions are the sole metamoderation mechanism on Hacker News — they work abysmally for managing good-faith users having a bad day or combatting spam, and there's an order of magnitude more of that than there are trolls.
The worst part is that HN's hellbanning isn't secret — you can just turn [showdead] on, defeating the point (see the "king of the shitpile" problem: http://metatalk.metafilter.com/1786/LPP-wall-of-shame). You'll see plenty of spam on the /new page, but for almost every [dead] comment you see you'll be baffled as to what happened. Sometimes it's just a duplicate post, and occasionally for hellbanned users you can page back through their history of good but [dead] comments and find a brief fit that could have been disciplined easily with a week's time out or even a simple admonishment to stop.
What really concerns me is all the individually-deleted comments and hellbanned users I've seen where there's no context at all as to why they're [dead] — the only thing I can think of is that they were eaten by the news.arc grue.
I understand what you're saying, that pg has every right to publish or [dead] or /dev/null our posts as he sees fit — but that's no reason for him to be cruel and capricious.