Those critics have less influence all the time. Some 18 states permit medical use of marijuana, and in November, Colorado and Washington voted to allow recreational use. Nationally, support for legalization is steadily rising. A decade ago, one of every three Americans favored the idea. Today, nearly half do -- and among those under 50, a large majority does.
These trends have diehard drug warriors screaming bloody murder. Former Rep. Patrick Kennedy, D-R.I., has formed a new organization to stop what he imagines to be the "300-miles-per-hour freight train to legalization." He says that such a change would be especially harmful to teenagers.
White House drug czar Gil Kerlikowske insists that even allowing medicinal pot "sends a terrible message" to adolescents. Mitchell Rosenthal, a psychiatrist who founded the substance-abuse treatment group Phoenix House, says there is "mounting evidence of the dangers it poses, especially to young users."
They might have a point if existing drug laws were keeping weed out of the hands of wayward kids. In truth, they're about as effective as a picket fence in a tidal wave. In a 2009 survey, high school students said they found it easier to get than beer. In 2011, 23 percent of 12th-graders said they had used weed in the preceding month.
In the past five years, drinking and cigarette smoking have dropped by more than 10 percent among high school seniors. But pot smoking has risen by 23 percent. Alcohol and tobacco are legal for adults. Marijuana is not.
What these trends indicate is that authorizing the sale and use of a substance does not necessarily mean more people will use it. There is no contradiction between letting adults make up their own minds, with some government regulation, and providing effective education for youngsters about the hazards of underage consumption.
No one, after all, is talking about putting pot in vending machines or handing out blunts at Taylor Swift concerts. The idea is to treat pot like booze -- permitting its sale and use to adults in a government-regulated market, with penalties for behavior (like driving under the influence) that endangers other people.
The tolerance-fuels-use theory is thunderously lacking in real-world support. In the Netherlands, where "coffee shops" are allowed to sell pot, teenagers are far less likely to use it than their American peers.