Rising crime rates during the 1980s led many Americans to demand that their political leaders do something to control crime. Politicians quickly discovered that passing laws requiring a mandatory minimum sentence for certain crimes— such as drug offenses, weapons violations, and murder—was very popular with voters. With the passage of these federal and state mandatory sentencing laws, criminals could no longer count on the leniency of the judge or mitigating circumstances to reduce their sentence.

Advocates of mandatory minimum sentences stress that the sentences are fair: Different offenders convicted of the same offense serve the same amount of time in prison. Judges are not be able to reduce (or increase) the sentence because of the criminal’s race, background, or gender. In addition, supporters contend that the tough sentences benefit society by taking criminals off the streets for...