As diaried on the Rec List, Attorney General Eric Holder is recognizing the long-building consensus that mandatory minimum sentencing for nonviolent drug crimes is producing an ineffective, unjust, and unsustainably large prison population full of people who don't deserve to be there. So perhaps now is the right time to ask the question: Should we institute a maximum prison population? And if so, what kind of policy should it be? An absolute numerical ceiling, a percentage of population, or some other basis? I would argue that we should have such a limit, regardless of which type we chose to go with.
Now you might say, "But what if more people commit crimes than the limit allows?" First, we need to recognize that if a major proportion of the population is committing crimes there is something else going wrong that isn't being solved by prosecuting them, and the two overwhelming culprits are either economics (i.e., they don't have viable alternatives) or the law itself being draconian and unjust. So imposing a limit on the prison population would force governments to at least partly begin to address these problems by mandating more stringent priorities.
And they don't really have a choice about what priorities they set: If they put a higher premium on throwing away nonviolent drug offenders than thieves and violent criminals, the crime rate would soar and political officeholders would be rightly blamed for it. So in many ways a maximum prison population would be drug law reform by other means, and also a check on other frivolous, draconian behavior by prosecutors, judges, and legislatures created simply for the sake of "tough on crime" posturing.
Even if an individual judge or prosecutor is an incorrigible sociopath and tried to still throw people away by the bushel for no reason, that doesn't mean the rest of the system would cooperate with them. Bureaus of Prisons and parole boards would deal on a daily basis with the logistical reality of running into the maximum, and soon "hanging judges" et al would become irrelevant laughingstocks for doling out long sentences that are instantly discarded by prison officials.
While the best approach to reform would be to legalize most currently illegal drugs and treat the few genuinely destructive ones medically, a maximum prison population could be one particularly effective angle from which to attack the War on Drugs. Such a policy would have cascading social benefits based on a very simple standard that, in addition, saves taxpayers vast amounts of money and makes the streets safer by refocusing police forces on violent crime.
That said, there are any number of corrupt, cynical, or ideology-driven ways that officials could sidestep these benefits. For instance, they could simply pour the resources currently going into prisons into supervised probation, ankle monitoring, drug rehab and psychiatric hospitals for people who really don't belong there either, and all the commercial interests that would be involved. That's a better and more humane authoritarian system than a vast prison state, but it's still an authoritarian system that would involve much of the same corruption and oppression.
But, again, it would be an improvement, and not every state would play that game: Some would genuinely just move to reform their drug laws and establish rational priorities, and others would have a mix of good and bad responses. Even the bad responses, however, would be better than the status quo.