Orin Kerr has an interesting post on how good comment cultures develop on blogs, based on a post here about comment sections at Concurring Opinions:
I’ve always believed that the comment sections of blog posts shouldn’t be wild west free speech zones. Ideally, the comments provide an interesting and thoughtful discussion, even where commenters strongly disagree with a post. Comments that are rude, off-topic, uncivil, and unnecessarily snarky or nasty don’t have much value in my opinion. It appears as though more and more bloggers are starting to get fed up with obnoxious comments. A few years ago, it seemed to me that the blogosphere had a much more permissive view toward comments than it does now.
I’ve noticed too that comment threads on blogs have gone downhill a good bit in the past few years as well. Â I think Professor Kerr is correct in his assessment of the reason:
I suspect the explanation rests largely on the different moderation practices at different blogs. If a blogger doesn’t moderate comment threads at all on a widely read blog, people who want to be shocking, mean, or just irrelevant realize they can do their thing and reach a decent-sized audience.Â
I’ve thought more often lately of moderating comments here, and deleting the really nasty, irrelevant or nutty stuff.  When I say nutty, I mean incoherent more than extreme.  I have no problem with extreme viewpoints, as long as people can make a case for them without devolving into nastiness (I should note I consider blatant racism nastiness).  But the real risk that I think you run with moderation is chilling discussion, because everyone is afraid of saying the wrong thing, or taking a strong stance for or against something.
I think moderating individual comments probably makes more sense than banning users from commenting. Â The worst a commenter need worry about is that his particular comment will get moderated. Â I think that probably has a far less chilling effect, and the lack of nastiness will probably encourage more thoughtful comments. Â If I do decide to implement moderation, I will do my best to post guidelines in the comment section, much like The Volokh Conspiracy does.
I cull stupid or profane comments without a second thought on both my blog and Youtube account.
I think that Belmont Club has the best comment section of any blog that I am aware of. Mr Fernandez has a somewhat opened way of writing posts that invite constructive follow up from knowledgeable commenter.
For most blog posters however the greatest comment problem, is the commenter that is trying to take over a blog that belong to somewhat else. They constantly post as if every post by the owner is something that they must refute and take down.