Earlier this week, New York City Police Commissioner Bill Bratton made a very confused statement about the increasingly popular movement to legalize marijuana. “Here in New York City,” he declared, “most of the violence we see, violence around drug trafficking, is involving marijuana. And I have to scratch my head as we see many states wanting to legalize marijuana, and liberalization of policies.”

As Jacob Sullum notes, “Bratton is presenting an argument for legalization as an argument against it … what Bratton views as a head-scratcher—that people would want to legalize a business tied to black-market violence—is actually a no-brainer.” Insofar as the marijuana trade is violent, it is because selling the drug is illegal. Prohibition gives rise to highly profitable conspiracies of criminals who vie for territory, using violence to best rivals who cannot turn to the law to defend themselves.

There may be costs to legalizing marijuana. Some people think that they outweigh the benefits. But there’s no question that legalizing marijuana would shift sale of the drug from criminals who sometimes engage in violence to businesses that almost never would. Legalization is the only effective way to eradicate such violence. How can one of America’s most successful police chiefs fail to understand that?