“Middle-class kids don’t get locked up for smoking pot, and poor kids do,” Mr. Obama added. Actually, almost nobody gets locked up for pot. Americans collectively smoke for three billion days a year and use has increased 38% since 2007, according to a Rand Corp. analysis of federal health survey data, yet there were merely about 750,000 marijuana-related “arrests” in the U.S. in 2012. In the official FBI statistics that can mean anything from a ticket or summons to a full booking.

Very few people are incarcerated for simple possession, which makes up about 88% of arrests. There are currently about 40,000 state and federal prisoners serving time for marijuana-related convictions, and most have violent criminal histories. Most judges must be persuaded that someone is a true danger to society to sentence prison for mere drug use.

Mr. Obama is also kidding himself if he thinks drug legalization will be a boon to the poor. His own history of drug use is well known, but most users aren’t the privileged students of the Punahou School. Like all human vices, the misery of addiction is always worse for those who lack the resources and family support of the affluent.