They see the result, but they are blind to the cause of it. Forty million more Americans than we had in 1950. If one person in fifty has a tendancy towards murderous violence, then we've got eight hundred thousand more of them now. And density alone affects the frequency with which mobs form. The intelligence of a mob can be determined by dividing the lowest IQ present by the number of people in the mob.
Life gets cheaper.
Cops, on a per capita basis, get fewer. And the imponderables of the bomb, of automation, of accelerating social change create a kind of urban despair that wants to break loose and crack heads. They should hark to the locust. When there is only a density of X per acre, he is a plain old grasshopper, munching circumspectly, content with his home ground. Raise it to 2X and an actual physical change begins to occur.