Agree completely. I think a counterpoint to that is that escalations can happen quickly and out of nowhere. Even if you show great restraint, a gesture that seems innocuous to you might set someone off. This could include a polite "toot" of the horn, pulling around someone in traffic legally, but too close for their comfort, etc.I agree with that, but I think one should practice a high level of restraint, regardless of whether one is carrying. Imagine the story you told, except "A" didn't have the gun. He probably would not have been prosecuted, but he may well have gotten the stuffing beaten out of him.
The rule I'd suggest is: before getting into a confrontation of any kind, consider what you stand to gain by it. In the vast majority of cases, there's nothing to be gained and no reason to engage at all; but (as I said in the other thread) humans are wired to puff out their chests when they don't like what others are doing.
I changed lanes on a four-lane not too long ago, following all the rules: I was paced with the traffic in the other lane, I was lined up with a space that offered plenty of room and I signaled. The driver behind me honked and flipped me off. He may have thought that I was too close, but my move was absolutely no threat to him in any way. If he had gone all road rage, followed me to my destination and came at me with a weapon, I wondered how the legalities might have turned out.
I ride a motorcycle. It is well known that some people take great offense at anything a motorcyclists do that they perceive as out of line, much more so than they would with someone in a car. Some people are just looking for some reason to harass a biker. I don't know why that is, but it is well documented. Also, you don't have much protection against a road rager if you are boxed in at a light. There is no car around you. So if someone comes at you, you pretty much have to take some radical action or you are toast. I am not sure where I am going with that, but I think about it a lot.