My colleague John Pfaff from Fordham (who is quoted extensively in Chapter 1 of Cheap on Crime) is an economist, and has tested the various explanations given for mass incarceration. His conclusion: the main cause for prison growth was not an increase in sentencing or the war on drugs. The problem is prosecutorial discretion.
"I understand where they come from. It’s true that legislators have passed a lot of new, tougher sentencing laws over the past 30 or 40 years. And it’s true that we have increased the attention paid to drugs. But in the end, there are other things that play a much, much bigger role in explaining prison growth. The fact of the matter is in today’s state prisons, which hold about 90 percent of all of our prisoners, only 17 percent of the inmates are there primarily for drug charges. And about two-thirds are there for either property or violent crimes."
. . .
"What appears to happen during this time—the years I look at are 1994 to 2008, just based on the data that’s available—is that the probability that a district attorneys file a felony charge against an arrestee goes from about 1 in 3, to 2 in 3. So over the course of the ’90s and 2000s, district attorneys just got much more aggressive in how they filed charges. Defendants who they would not have filed felony charges against before, they now are charging with felonies. I can’t tell you why they’re doing that. No one’s really got an answer to that yet. But it does seem that the number of felony cases filed shoots up very strongly, even as the number of arrests goes down."