I can think of three benefits from people being civil, in arguments about economics (for example).
1. It is hard for people to change their minds. If you have always seen the world as a duck, it is hard to see it as a rabbit. It is even harder to admit you were mistaken, and that the world really is a rabbit (perhaps for psychological reasons, or perhaps because it's a signal of your propensity to make mistakes). It is easier for people to change their minds if an argument is civil. It is (relatively) easy to say "I was not aware of that data, or that argument, and I admit it now does look like a rabbit". It is much less likely that someone would change his mind after being accused of intellectual dishonesty, being a paid shill, or being psychologically disturbed, because changing his mind could then be interpreted as confessing to the accusation. Instead, he is more likely than ever to insist he is right. We are less likely to get the economics right if people find it harder to change their minds.
2. We could settle arguments about economics with guns. (A lot of 20th century history is about how people settled economic arguments with guns.) But trial by combat is not a good way to settle arguments about economics, because there is probably a low correlation between being right and being proficient with guns. There is probably an equally low correlation between being right and being proficient at verbal bullying. (This is not a slippery-slope argument that incivility leads to violence, which would be a fourth benefit to civility, but an argument by analogy.) We are less likely to get the economics right if success in argument is determined by relative proficiency in making and withstanding personal attacks.
3.Getting economics right is important for improving human welfare and/or human rights. (Or at least, economists like to think it is.) Incivility per se detracts from human welfare and rights.
That's all I can think of.
Sometimes, like today, it is more important than usual that the right side wins the economic argument. That makes civility more, not less important than usual. We do not know, a priori, which side is right. (A posteriori, a lot of people who thought they were right have turned out to be wrong).
I am going to make just one empirical observation about civility on the internet (and I bet it's not what you are expecting). I hang out on economics blogs, and I have also spent a lot of time hanging out on car forums (hey, we all have our hobbies, and there's something deeply satisfying and stress-relieving about helping some Australian replace his alternator). As you might expect, the people on the car forums are predominately young, male, and their average level of education is lower than those who hang out on economics blogs. Just the sort of people you might expect to get into fights. The issues at stake (getting their car running, or running faster, and their reputations as shade-tree mechanics) are as important to them as the issues on economics blogs. The occasional fight does break out (torque vs horsepower, VTEC vs. V8 , the ethics of street-racing, does this look "rice", is it OK to call cars "rice", etc.), but on balance the car forums are at least as civil as the economics blogs.
And I apologise to those to whom I have been uncivil.
And sorry for a prissy post.
Worthwhile Canadian Initiative 
Politics blogs are substantially less civil. I don’t know why this should be the case (when compared to economics, or cars).
Andrew: it looks that way to me too. We have to be careful of our biases though. It’s always easier to see incivility in others. That’s partly why I chose car forums to compare to economics blogs. As both a car-nut and an economics-nut, I have a dog in both races, so am less likely to be biased.
Keynes repeatedly belittled Hayek’s work in the most uncivil terms — without substantive argument attached.
All sorts of other top Keynesian economists — like Samuelson and Galbraith — seemed intentionally to slanderously mischaracterize Hayek’s work as a means for marginalizing both Hayek and “free market” economics.
This approach seems to have set a standard of behavior for some later-day Keynesians such as Krugman and DeLong.
The tone among economists has been set right at the top.
Greg: maybe, but again let’s watch for our…what’s that biblical quote about motes and beams?
Maybe it’s that we are all just stuck in a bad equilibrium, and need a “Keynesian” “nudge” out of it.
But yes, it’s most important that the best economists set a good example. The rest of us will try to copy them, and may be more successful at copying their style than their substance.
There’s a central problem — or a confluence of problems.
The first is that how to provide sound economic explanations is an essentially contested problem — and attempts to end that conversation with the “objective” methods of mathematics and “testing” has not only failed on the terms originally proposed by advocates of these means, but in the view of many these methods themselves have merely begged the question and blinded economists to the scientific fallacies of their own approach to economic explanation.
When academics “inhabit” essentially different worlds, with different standards of “what is good”, they don’t tend to fight fair, and they don’t tend to even pretend that “the other guy” is worth paying attention to — instead they actively work for the advance of their own approach and against that of others, and almost always this involves a good bit of mischaracterizing and disparaging of “the other guys”.
In the early 1960s at the University of Virginia this went so far as the firing of economists like Ronald Coase, James Buchanan, and Leland Yeager, in an effort to remake the economics department as a cutting edge “scientific” economics department which would be supported by the major Foundations and the NSF, etc. And in the last two decades every top economics department has eliminated its history of economic thought requirement and cut most of its classes in this area.
This non-verbal “incivility” has been matched by all sorts of marginalizing verbal stuff directed at “unscientific” economics and “scholastism”, et.
The other side of is that for many, the attraction of economics in the first instance was an attraction to a field that promises political relevance in the project of making a better world. For many economists, economics is part of their ethics and their politics, part of their identity. It’s ethical politics and identity politics by other means. It’s good guys vs. bad guys.
When you cross essentially contested visions of good explanation/good science with the identity emotions of ethics and politics, you’re tapping into the parts of human beings that leads folks like Samuelson or Galbraith to belittle and mischaracterize the work of someone like Hayek for the purpose of marginalization.
I don’t think this sort of incivility is going away any time soon, no matter how we admire good role models like Russ Roberts or Ben Bernanke.
Probably, the firing of Coase, Buchanan and Yeager (I hadn’t known they were fired, by the way) seemed like a good idea at the time!
One of the best parts for me about taking History of Thought (just one class, and I never had the head for it) was being forced to realise just how fallible economists were, and therefore how fallible we probably still are. And how the scope and method has changed over time. I remember my naive question to the prof (David Laidler): “What’s this Malthus stuff on population got to do with economics, anyway?”. That gave him a good “teaching moment”!
Every economics student should be so lucky as to have Laidler as an instructor — his book Fabricating the Keynesian Revolution is terrific.
Concerning Malthus, think how many economists in the 60s and 70s could have imaged you could do economics like Gregory Clark?
Economics is hard.
Imagining that its easy because you’ve mastered some (relatively) easy mathematics doesn’t make it easier, as I’d wager most economist believe.