I am not sure I understand why violence is "irrational" (as opposed to "unacceptable" or just "bad." As I understand it, rationality has no part in determining the end, just the means by which it is sought. So if the end is to make yourself feared and respected, or to be let alone in rough company, violence may very well be a rational means to that end. Depending on circumstances, like, are you on a tough street or at an academic convention. At the convention, physical violence would be self defeating.

Mark: Rhodes likewise believes soldiers don't normally want to kill or shoot to kill, and he cites a scholar who examined the muskets abandoned on the field in the Civil War, and found that a large number were still loaded, or even loaded many times. He concludes that soldiers loaded their muskets to look diligent, but did not fire them.
I have problems with that.

1. One assumes that soldiers who abandoned muskets were those not keen on shooting them. What about muskets that weren't abandoned?

2. The fact that a musket is loaded does not prove that it wasn't fired. And a person reluctant to kill could as well fire his musket in the air. And yet, it is notoriously true that those muskets were used with murderous accuracy. A whole lot of people were shot in the Civil War.

3. My father remarked that in World War II, a lot of soldiers never fired their rifles. He attributed that to a lack of visible targets. He said he remembered a speech by General Patton, who told the troops to think where they would be if they were Germans, and shoot there. After the speech, Patton asked him what he thought, and he said (very respectfully) he thought it was a fine idea, but doubted the troops would actually do as the General said. But, he said, he was wrong, and Patton was right, because after the speech there was a great deal more shooting, and also more effective shooting.

4. It seems to me Grossman is looking at things through a distorting ideological glass. I don't believe any amount of military training can make a person kill if he really doesn't want to. On the other hand, shooting pop-up targets might just convey the idea of shooting where there is movement, even if no clear view of a person or object. I find it extremely hard to believe that shooting at pop up targets will overcome even the weakest moral reluctance to kill.