Our marijuana laws are clearly doing more harm than good. The criminalization of marijuana did not prevent marijuana from becoming the most widely used illegal substance in the United States and many other countries. But it did result in extensive costs and negative consequences.

Law enforcement agencies today spend many billions of taxpayer dollars annually trying to enforce this unenforceable prohibition. The roughly 750,000 arrests they make each year for possession of small amounts of marijuana represent more than 40% of all drug arrests.

Regulating and taxing marijuana would simultaneously save taxpayers billions of dollars in enforcement and incarceration costs, while providing many billions of dollars in revenue annually. It also would reduce the crime, violence and corruption associated with drug markets, and the violations of civil liberties and human rights that occur when large numbers of otherwise law-abiding citizens are subject to arrest. Police could focus on serious crime instead.

The racial inequities that are part and parcel of marijuana enforcement policies cannot be ignored. African-Americans are no more likely than other Americans to use marijuana but they are three, five or even 10 times more likely—depending on the city—to be arrested for possessing marijuana. I agree with Alice Huffman, president of the California NAACP, when she says that being caught up in the criminal justice system does more harm to young people than marijuana itself. Giving millions of young Americans a permanent drug arrest record that may follow them for life serves no one's interests.

Racial prejudice also helps explain the origins of marijuana prohibition. When California and other U.S. states first decided (between 1915 and 1933) to criminalize marijuana, the principal motivations were not grounded in science or public health but rather in prejudice and discrimination against immigrants from Mexico who reputedly smoked the "killer weed."