James Q. Wilson is interviewed on crime in the 1960s in the First Measured Century:
Between 1963 and the early 1970s, the rate of violent crime more or less tripled in the United States. By “violent crime” I mean murder, manslaughter, and robbery and assault. So we had a tripling of the crime rate at a time when the country was by and large prosperous; [and,] except for Vietnam, more or less peaceful; in which the unemployment rates, even among African American adolescents, was really quite low.And this change occurred in part because the population was getting younger, though nobody had predicted this in advance. In retrospect it turned out that the youth of the population does contribute to the crime rate. But that wasn’t the whole story. Our population getting younger probably explains no more than 15 or 20 or 25 percent of the increase.
The rest of it was explained by two other factors: one that is easy to describe — namely, we had stopped sending people to prison. The prison population in the 1960s declined. It was lower at the end [of the decade] than it was at the beginning, even though the crime rate was going up.
The other is harder to describe and impossible to measure. And that is the ethos, the culture of the country, had changed. The notion of “do your own thing,” “strike out on your own,” “turn on, tune out, drop out.” These slogans, this attitude of radical self-indulgence, had affected a significant fraction of the population, and this weakened the ordinary social constraints that were operating on people.
(Hat tip to 2blowhards.)