IF someone is a genuine troll, then hell-banning is a great way of dealing with it, because it maximizes the time wasted by the troll and minimizes the time used by the moderator.
However, if the person isn't actually out-and-out to mess with your site, it sucks. I've seen lots of communities go down the tubes because the moderators get busy with life, and then Something Happens On The Forum, and moderators passive-aggressively go "fine, we're just gonna act like this, and if you don't want us to do that, then you should make the community act better!" Basically announcing that they are going to put in minimal effort to moderation, and the community definitely notices.
Professional moderation, like HN uses, seems like the best way to go.
Indeed, it's a situation where the needs of the many (HN community as a whole) outweigh the needs of the few (banned non-troll commentators). The danger lies in becoming such an elite, closed group due to blind moderation and banning even the most innocent members over a perceived slight, that the moderators themselves end up the trolls of what is left of the community.
For example, there's a certain GNU/Linux distro that is maintained by a core group of devs who have become overtly hostile to any new users of their project, and actively seek to discourage "newbies" from seeking help and getting any benefit out of the project. One would think the toxic atmosphere would have killed the distro off long ago, yet it's maintaining popularity and even seeing an uptick in a certain niche community. I certainly don't understand how it thrives with such a rotten core; yes, it's overall a very well done distro, but even the best product normally can't survive that kind of cancer.
That's not to say that HN would ever end up like that; indeed, from what I've seen they are doing an excellent job overall with maintaining and moderating this community. I just hope it continues to stay that way or improve, instead of going down a dark path towards chaos.
However, if the person isn't actually out-and-out to mess with your site, it sucks. I've seen lots of communities go down the tubes because the moderators get busy with life, and then Something Happens On The Forum, and moderators passive-aggressively go "fine, we're just gonna act like this, and if you don't want us to do that, then you should make the community act better!" Basically announcing that they are going to put in minimal effort to moderation, and the community definitely notices.
Professional moderation, like HN uses, seems like the best way to go.