Freakonomics holds a quorum on decriminalizing pot. Jeffrey A. Miron, director of undergraduate studies at Harvard University’s economics department:
Legalization would benefit the public purse. My research indicates that legalization would save federal and state budgets approximately $13 billion in enforcement costs and allow collection of about $7 billion in tax revenues, assuming marijuana were taxed like alcohol and tobacco. One thing legalization would not do is produce a major increase in marijuana use; existing evidence suggests prohibition has only a modest impact. Alcohol consumption declined moderately but not dramatically during alcohol prohibition, for example.