Today’s Washington Post contains a Ruth Marcus interview of Nora Volkow, head of the National Institute on Drug Abuse.
Volkow opposes marijuana legalization; she believies it will generate a large increase in use, which will (allegedly) harm users and society.
No one knows how much use might increase under legalization; existing evidence suggests a modest change, but since few countries have fully repealed their drug (or alcohol) prohibitions, we do not have decisive evidence.
The fact Volkow ignores, however, is that if use increases substantially, this means many people perceive a significant benefit from increasing their use or from initiating use; that is a positive of legalization, not a negative!
Marijuana use can, of course, generate unwanted side effects, but Volkow exaggerates these enormously. And other goods, like alcohol, also generate negative spillovers; yet we keep them legal (in part) because they generate substantial benefits.
Volkow further ignores the fact that prohibition generates its own negatives, such as violence, corruption, poor quality control, civil liberties infringements, medical restrictions, enforcement costs, and foregone tax revenue (which forces other tax rates to be higher).
So even if legalization means far greater use, and even if this generates undesirable consequences, the sum of benefits for current and prospective users, combined with elimination of prohibition’s costs, makes legalization the right choice.