I don't know a method to force civility on people as they discuss contentious political topics.
Ummm... make them go stand in the corner and consider the error of their ways? (Translation: yeah, ban them for a month or two, and do it fast
Ask a kindergarten teacher about this kind of behavior.
As a couple of people have now pointed out, one reason for the (childish!) incivility is that there's so much of it out there in the general culture, especially the political culture. The notion that politicians, journalists, and commentators ought to focus on facts and ideas rather than lies and invective has come to seem a bit old-fashioned. It's so much more satisfying to rant, and, unfortunately, appealing to people's fears -- and other emotions -- is politically effective.
The moderators try very hard to maintain some sort of standard of civility and of sensible discourse -- and I completely understand if they've come to feel, over the past few months, that it's like... oh, standing in the path of Hurricane Katrina and trying to turn it back. But a forum like this could -- in theory -- be a place where people who dislike this trend try, by example, to make the case that it doesn't have to be that way. It's probably a losing battle, in terms of the general culture, but if even a few people can be won over to the idea that it's at least
as satisfying to make a point logically and respectfully as it is to try to make it by name-calling, fear-mongering, spreading malicious rumors, etc. -- then the effort seems to me to be worthwhile.