Lost among the last-days rush of opinions in the U.S. Supreme Court (on affirmative action, voting rights and same-sex marriage) is one that nibbles at a very large criminal-law problem.

On June 17, the court made federal sentencing a little more sensible. In Alleyne vs. United States, it overturned precedent and held that the facts supporting a mandatory minimum sentence must be found beyond a reasonable doubt by a jury (or agreed to in a plea agreement), rather than simply being determined by a preponderance of the evidence by a judge.

Alleyne didn't get rid of mandatory minimum sentencing provisions, which remain criminal law's bluntest instrument. Those harsh statutes will still bind judges' hands and continue to produce outlandish sentences, particularly in narcotics cases. Prosecutors simply will prove the predicate facts at trial or (more commonly) include them in plea offers.

The use of these tough, arbitrary and thoughtless provisions is a driving force behind our mass-incarceration problem. Defendants caught with just five grams of methamphetamine, for example, face a mandatory sentence of five years imprisonment in a system without parole. It takes 20 times as much heroin to trigger the same mandatory minimum sentences.

In fact, more than 80 percent of all persons charged with meth offenses in federal court last year were eligible for five- and 10-year mandatory minimum sentences. These sentences can easily double if the person has a prior drug offense (no matter how old) that may even have been a misdemeanor under state law for which the person paid only a small fine and did not even serve one day in jail.

With two such priors — even with no jail time — a defendant can receive a life sentence with no possibility of release except through an extraordinarily rare presidential pardon or commutation. Such harsh sentences might be justifiable if they solved a problem, but there is no evidence that they do so. Rather, they create incentives to target and incarcerate very low-level offenders who are easily replaced in a system with almost no barriers to entry.

The human cost of this system is real and tragic. Over the past several years one of the authors of this article — Judge Bennett — has visited, in their federal prisons, more than 250 of the defendants he has sentenced. The vast majority of these inmates were very low-level, nonviolent drug addicts who were subject to mandatory minimum sentences.

Many of their families lost their homes and were forced to go on welfare. Most inmates made substantial strides toward improving their education, learning a trade and going through intensive drug treatment. But those with the longer mandatory minimum sentences sometimes give up hope, and they only thing they learn is how to commit more serious and violent crimes. Having lost all family ties, they are at much higher risk for reoffending when they get out.

Certainly, mandatory minimums are only part of the problem. President Obama's strange reluctance to commute sentences, even when the law has been changed relating to the underlying crime, exacerbates the problem. So do overzealous prosecutors and judges who don't seek balance between retribution and problem-solving. Mandatory minimums, though, may be the most likely target for reform even after Alleyne: A bill in Congress, the proposed Justice Safety Valve Act, would give judges more leeway to set aside statutory minimums where appropriate.

In the end, such reforms should succeed because they are consistent with our national character. We treasure freedom, and mass incarceration restricts freedom without an offsetting benefit. It is shocking that the United States incarcerates more persons per capita than North Korea, China, Russia and Iran.

In fact, this country has the highest incarceration rate in the world, and more than 50 percent of the inmates in federal prisons are nonviolent drug addicts. In moving forward, our efforts to combat drug abuse and trafficking should be more creative and less retributive, and should align with our own best selves as a freedom-loving nation.

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Mark W. Bennett has been a federal judge in the Northern District of Iowa since 1994. Mark Osler is a former federal prosecutor and a law professor at the University of St. Thomas in Minneapolis.