Now imagine that you have a pistol on the seat next to you. It changes your perspective. "If that guy knew what I had here..."
I think Robert Heinlein had it right when he wrote, "Well, in the first place an armed society is a polite society. Manners are good when one may have to back up his acts with his life. For me, politeness is a sine qua non of civilization. That’s a personal evaluation only. But gunfighting has a strong biological use. We do not have enough things to kill off the weak and the stupid these days. But to stay alive as an armed citizen a man has to be either quick with his wits or with his hands, preferably both. It’s a good thing"