Ross Douthat lauds the success of mass incarceration at contributing to reduced crime rates, but rightly observes that the time has come to ease up on this enormously ethically problematic approach:
But as you might expect, a policy turn undertaken during a period of emergency will eventually produce diminishing returns — as Steven Levitt puts it, “the two-millionth criminal imprisoned is likely to impose a much smaller crime burden on society than the first prisoner” — even as it imposes substantial moral costs. And precisely because the tough-on-crime approach was largely vindicated by events, it’s extremely difficult for elected officials to walk back from some of the dubious practices that have grown up around it — like, say, the possibly cruel-and-unusual use of long-term solitary confinement.
I think the most promising solution here is to replace funding for ever-growing prisons with funding for other measures that are just as indubitably “tough” on crime. Most of all, more police officers. At this point, there are very good reasons to believe that an extra cop would have more crime control impact than additional prisoners, and preventing crime by having cops on the street deterring bad behavior and perhaps convincing criminals to find some other way of getting money is a lot more socially beneficial than preventing crime by letting criminals commit bad acts, and then locking them up for years.