It's a genuine problem and has been growing gradually worse for a while. I think the cause is simply growth. When a good community grows, it becomes worse in two ways: (a) more recent arrivals don't have as much of whatever quality distinguished the original members, and (b) the large size of the group makes people behave worse, because there is more anonymity in a larger group. I've spent many hours over the past se…
The thing about systems is that we tend to think of them as if people are not a part of them. But people are a part of them.
One thought I would suggest is that it might be worth giving people with very high karma (maybe high enough that only a few people have this) an ability to post highlighted reprimands, and an automatic banning of a user if he or she gets more than, say, 5 of these in a month. These could then be reviewed of necessary.
One thing I would think about is that rather than having a system where computers try to control people, have a system which empowers the community leaders to set standards of interaction.