James Q. Wilson has this op-ed in the Sunday LA Times, responding to the Pew report about 1 in 100 in prison and the accompanying hullabaloo.

In the last 10 years, the effect of prison on crime rates has been studied by many scholars. The Pew report doesn't mention any of them. Among them is Steven Levitt, coauthor of "Freakonomics." He and others have shown that states that sent a higher fraction of convicts to prison had lower rates of crime, even after controlling for all of the other ways (poverty, urbanization and the proportion of young men in the population) that the states differed. A high risk of punishment reduces crime. Deterrence works.

But so does putting people in prison. The typical criminal commits from 12 to 16 crimes a year (not counting drug offenses). Locking him up spares society those crimes. Several scholars have separately estimated that the increase in the size of our prison population has driven down crime rates by 25%.