I've been participating in online community discussions for about 35 years now (starting with the Plato System in 1974.) I've seen numerous discussion groups start, grow, become diseased (with trolls, hostile opponents, etc.), recover, mature, senesce, and die.
I was among the first on Usenet Groups (which were an imitation of the newsgroups on the Plato System), and if you want to read some of my early (1984) Usenet postings, search google groups for "Huybensz" (my maiden name, which nobody ever pronounced or spelled correctly, now shortened to Huben) or "mrh". Google's cache of early postings is very incomplete.
So when moderation policy issues come up, I do think I know something about it. Sometimes they have come up here, sometimes people who dislike my position or style bring them up in their own blogs.
Here, as a heuristic, I tend not to allow anonymous comments. It is trivial to create a pseudonymous google (or other) identity: that's no real obstacle, despite protests from fools like Skeptico. It does deter the most casual annoying commenters. But the big win is that it allows us to have lines of argument person by person, rather than a contradictary chorus of an anonymous crowd.
I also rarely delete comments. I'm reluctant to do so, but sometimes there are good reasons that are not encapsulated by simple rules.
The best explanation of managing comments in blogs that I've seen is from Teresa Nielsen Hayden, her post NOT titled Some things I know about moderating conversations in virtual space.
Here are her principles:
1. There can be no ongoing discourse without some degree of moderation, if only to kill off the hardcore trolls. It takes rather more moderation than that to create a complex, nuanced, civil discourse. If you want that to happen, you have to give of yourself. Providing the space but not tending the conversation is like expecting that your front yard will automatically turn itself into a garden.
2. Once you have a well-established online conversation space, with enough regulars to explain the local mores to newcomers, they’ll do a lot of the policing themselves.
3. You own the space. You host the conversation. You don’t own the community. Respect their needs. For instance, if you’re going away for a while, don’t shut down your comment area. Give them an open thread to play with, so they’ll still be there when you get back.
4. Message persistence rewards people who write good comments.
5. Over-specific rules are an invitation to people who get off on gaming the system.
6. Civil speech and impassioned speech are not opposed and mutually exclusive sets. Being interesting trumps any amount of conventional politeness.
7. Things to cherish: Your regulars. A sense of community. Real expertise. Genuine engagement with the subject under discussion. Outstanding performances. Helping others. Cooperation in maintenance of a good conversation. Taking the time to teach newbies the ropes.
All these things should be rewarded with your attention and praise. And if you get a particularly good comment, consider adding it to the original post.
8. Grant more lenience to participants who are only part-time jerks, as long as they’re valuable the rest of the time.
9. If you judge that a post is offensive, upsetting, or just plain unpleasant, it’s important to get rid of it, or at least make it hard to read. Do it as quickly as possible. There’s no more useless advice than to tell people to just ignore such things. We can’t. We automatically read what falls under our eyes.
10. Another important rule: You can let one jeering, unpleasant jerk hang around for a while, but the minute you get two or more of them egging each other on, they both have to go, and all their recent messages with them. There are others like them prowling the net, looking for just that kind of situation. More of them will turn up, and they’ll encourage each other to behave more and more outrageously. Kill them quickly and have no regrets.
11. You can’t automate intelligence. In theory, systems like Slashdot’s ought to work better than they do. Maintaining a conversation is a task for human beings.
12. Disemvowelling works. Consider it.
13. If someone you’ve disemvowelled comes back and behaves, forgive and forget their earlier gaffes. You’re acting in the service of civility, not abstract justice.