We live in a culture that says "if you disrespect me in any way, if you disagree with me over anything, if you cut me off in traffic, if you take my parking space/shopping cart/space in line, I will shoot you."
Somehow along the way, we have produced at least two generations of parents who forgot the part about teaching their young 'uns how to work out differences without being stupid or violent. Pre-school disagreements in the sandbox, taking someone's crayons in kindergarten, cutting in the water line in 3rd grade, knocking someone out of the way to board the school bus in 7th grade, bumping into someone in the high school hallway, the hangout location, or just riding down the road. None of these daily occurrences should be the source of tremendous rage, violence, death, and stupidity, but among at least two generations now, they are considered normal. Adults think nothing, nothing, of flipping their middle finger at rude drivers, setting a wonderful example for their children in the car and/or those nearby who witness this immature choice.
Again, it is not the weapon of choice, it is the individual reaction, the individual choice to the perception or reality of having been slighted. Mature people of any age can avoid violence with proper conflict resolution skills at almost any age.
This insanity can be prevented by proper education in the schools, if legal guardians at home can't do it. Far more important to learn this skill, than calculus or Spanish.