This also touches on one of my favorite essays on social software: A Group Is Its Own Worst Enemy ( http://www.shirky.com/writings/group_enemy.html )
In many cases, the community can do an acceptable job of moderating when given the tools to do so. There is often a core group within the community that tries to keep things sane. Back in the days of usenet, we had people who would moderate because they cared about usenet as a whole and their news groups in particular. Shared kill files, honoring their cancel posts... and for the most part, it worked.
Now days there are three different structures of social software that are dominating - and dealing poorly with trolling. There is the "the community does it all" but lacking the necessary tools to moderate. Reddit and Stack Exchange are the two that most obviously fill this domain - community moderators that scale very poorly. On the other hand you've got the "use a third party like discus" to host the comments. And frankly, that which has some significant lack of moderation tools for the people using it. On the third hand you've got the self hosted forums run by a company - news sites often have this. All moderation is done by the staff and that fails horribly in terms of making sure the comments are something that one wants to read.
While the don't feed a troll worked back in the usenet days where the entire community could ostracize the people (or actively remove their attention seeking ways by canceling messages or just not accepting those posts), those moderation tools haven't made it back into today's social software along with the ability to have a site that is able to be moderated by the community and has a strong enough core group to do the moderation without rapid burn out.
Don't feed a troll was an elegant weapon for a more civilized age. It meant much more than just ignoring them, and the tools to ignore them were more available.