Either Americans are the most evil people on Earth or there’s something terribly wrong with their criminal-justice system. We hope it’s the latter. With less than 5 percent of the world’s population, the United States has nearly 25 percent of the world’s prisoners. The U.S. locks people up at a rate nearly five times the world’s average. Since 1980, its inmate population has more that quadrupled.

How to explain? First, there’s the sad reality that U.S. crime rates, despite their general decline in recent years, are still far higher than those of other advanced democracies — stoked, perhaps, by the nation’s sharp social disparities and the easy access to firearms. Then there’s the sad reality that jails and prisons, rather than hospitals, are being used to warehouse the mentally ill. An estimated 16 percent of the nation’s inmate population suffers a mental disorder.

But among the causes, what’s drawing the most attention now are the harsh sentences handed down over the last three decades as part of the “war on drugs.” Competing to be toughest on crime, political leaders passed “three strikes” laws, imposed longer prison terms and prescribed mandatory minimum sentences even for nonviolent drug offenders. In some states, a first offense for marijuana possession brings 10 years in the slammer. Prisons are stacked with these nonviolent offenders, most of whom had the misfortune of growing up in poor, minority communities where the drug trade was part of ordinary life. While blacks and Latinos account for 30 percent of the U.S. population, they make up 60 percent of prisoners.

President Obama’s visit to an overcrowded federal prison near Oklahoma City last month drew attention to badly needed reforms. After peering into a spare 9-by-10-foot cell, which at times had housed three men, Obama told a group of prisoners that he could have easily been in their place if not for the advantages he enjoyed growing up. (Obama has admitted using marijuana and cocaine in his youth.) “There but for the grace of God,” he told reporters afterward, pledging to renew his reform efforts. “Mass incarceration makes our country worse off,” he said. “And we need to do something about it.”

Both parties are in rare agreement on that. Democrats emphasize the wasted lives and the damage to minority communities. Republicans stress the billions of dollars spent on locking up people who aren’t dangers to their fellow citizens.

It’s a stretch to suggest, however, that the bloated prison population is due mainly to the sentencing of nonviolent drug offenders. It’s not. Most of the increase comes from locking up greater numbers of thieves and violent criminals and keeping them behind bars longer. Even if all nonviolent drug offenders were set free today, the prison population of 2.2 million would drop to only around 1.7 million, still nearly 20 percent of the world’s total.

Still, on the margin, granting early release to nonviolent offenders and shortening sentences to better match crimes seems a sensible step for the federal system, and eventually for the states. Career criminals need to be locked up. But hundreds of thousands of nonviolent offenders have aged out of their youthful mistakes. Many deserve a second chance to remake their lives.

So, which is it? Are Americans the most evil people on Earth, or is their criminal-justice system seriously flawed? The answer isn’t so clear. To make real headway on the prison anomaly, thousands of murderers, robbers and other predators would have to be released early or receive shorter sentences. It’s doubtful that politicians or the public would be ready for that.