"Don't read the comments" is pretty common advice on the Internet, and for good reason: once somebody starts leaving snarky or rude comments others tend to follow suit. Blog owners or community moderators can clean them up later, but often the damage has already been done -- people get upset, your site looks bad, etc. On some platforms owners/moderators can screen all comments, requiring that they be reviewed before being posted, but that's not always possible or desirable (see below).
I am a moderator on a medium-sized Stack Exchange site. We get a lot of comments, and -- contrary to the common wisdom -- many of them actually are helpful, constructive, and timely, so we wouldn't introduce a time delay by moderating comments even if the platform allowed us to. But we also get those other kinds of comments, enough to be problematic, and because we don't have constant coverage sometimes a comment thread descends into chaos until a moderator comes along and cleans it up some hours later.
I am looking for cultural (not technical) ways to deter those negative comments in the first place, before they make a mess. What should we do in how we present our site, or in how we engage users (new or otherwise), to make them less likely to want to post disruptive comments? Are there relevant sociological or psychological techniques we should be using?
A few notes:
We can and do take corrective action against users who show a pattern of this kind of behavior.
Stack Exchange uses a reputation system and users must reach a certain fairly-low reputation level in order to be able to comment. This threshold is not adjustable. (It does a good job of fending off spammers and drive-by snipers.)
Users can flag inappropriate comments and moderators rely on these flags to know where the "hot spots" on the site are. With very few exceptions, only moderators can delete comments.
We have a worldwide community.