The intuition behind the incarceration theory goes something like this: "If criminals are locked up, they cannot be out on the streets committing more crimes. Plus, once they get out of prison, they'll think twice before committing another crime." Sounds simple, yet intuitive at face value. Economist Steven Levitt wrote a paper in 2004 examining the crime rate decrease, and found that up to 58 percent of the decrease in crime rates since the early 1990s could be attributed to incarceration. However, Levitt has even conceded (Stemen, 2007, p. 8) that focusing on drug offenders instead of hardening criminals has a crowding out effect that minimizes prison's efficacy. The other issue is that Levitt's data set ends at 1993, which is when the crime rates just started to precipitously decrease. With that, let's take a look at the relation between incarceration and crime rates, like the Brennan Center did [below] (Roeder et al., p. 16).
Even if we were to assume the unlikelihood that incarceration was the sole factor in reduced crime rates, looking at the correlation suggests that the effect started to wear off by 1997. However, this is a very simplistic way of looking at it because correlation is not the same thing as causation. As the report points out, the crime rates didn't decrease as soon as the incarceration rates increased (p. 25). If increased incarceration was so vital, why did it take well over a decade after the "tough on crime" policy for it to kick in? Questions like these is probably why the report's findings were even less generous than one would have anticipated:
"Since 2000, the effect of increasing incarceration on the crime rate has been essentially zero. Increased incarceration accounted for approximately 6 percent of the reduction in property crime in the 1990s, and accounted for less than 1 percent of the decline in property crime this century. Increased incarceration has had no effect on the drop in violent crime in the past 24 years. In fact, large states such as California, Michigan, New Jersey, New York, and Texas have all reduced their prison populations while crime has continued to fall (p. 15)."
If the main benefit of mass incarceration is supposed to be a reduced crime rate, then this is a pretty damning statement of the criminal system. Why? Looking at the U.S. prison rates with a state-by-state breakdown, and then comparing that to other countries, is not flattering. How did we get to a point where our incarceration rate is so high that it shadows that of China, which is a massive human rights abuser known for incarcerating political dissidents? There's also the matter of the price of incarceration. Crime doesn't necessarily pay, but the taxpayer is paying a pretty penny for higher incarceration rates. According to the Brookings Institution's 2014 study on incarceration, we went from paying $17B in 1980 to $80B in 2010 in 2010 real dollars. That is more than quadruple the amount at the beginning of the 1980s! The fact that incarceration typically makes it on the Top Three list for largest expenditures on state budgets doesn't help any, either.
Although incarceration helps when we lock up the hardened criminals, it decidedly has a diminished effect when we lock up non-violent offenders, most notably drug offenders who mostly likely were busted for marijuana possession. This is why the Brennan report points out the effect of diminishing returns. When you lock up those who are not a real threat to society, the marginal crime-reduction gains drop substantially, which is precisely what has happened in the case of incarceration in the United States (p. 17, 19, 22). Aside from the overuse of incarceration, there is also the issue of lousy prison conditions that might actually harden prisoners even more (p. 24), which brings me to my next point.
Recidivism, which is the rate at which criminals reoffend, is still a concern because in 2005, the National Institute of Justice found that three-quarters of prisoners were rearrested within three years. Using the recidivism rate from this time period (as opposed to the current recidivism rate) is better because it will capture some of the more hardened criminals from the 1990s, which is when the crime rates really started to drop. It also doesn't help that being in prison creates stigma and social barriers that make it more difficult for former prisoners to find a new job and start a new life (Visher et al., 2010). And let's not even get into how this affects communities and families, and disproportionately so for those who are poor and uneducated (Subramanian, Ram et al., 2015).
The moral of the story here is that incarceration beyond America's worst criminals is bad policy because it does little to nothing to improve public safety (McCrary and Sanga, 2012). Canada had a similar drop in the crime rate in the 1990s to the United States, but Canada's incarceration rate actually decreased. America should be ashamed that it houses nearly a quarter of the world's prisoners while only making up for less than five percent of the world's population. If the Right-leaning Heritage Foundation thinks that we have reached a point that criminalization has gone too far, then there there has to be something do with regards to sentencing reform, or better yet, abandon the War on Drugs and the "tough of crime" mentality, both of which have been abject failures. Mass incarceration is an ineffective policy that creates all sorts of fiscal and social costs. I hope politicians can get out of the "tough on crime" mentality for long enough to realize that crime reduction policy needs to be much better targeted than what we have right now. That way, they can stop ruining lives while simultaneously passing the costs onto the taxpayer.