Intravenous-drug users who spread disease by sharing dirty needles and engaging in unprotected sex are responsible for more than a third of all the AIDS cases in the United States and more than half of the new cases of hepatitis C. Addicts will continue to drive these epidemics until the country takes a more enlightened approach to drug treatment. That means discarding the laws that criminalize needle possession because such laws encourage addicts to share needles. It also means developing large-scale treatment programs that admit addicts right away instead making them wait months or years. A blueprint for such a...