So how come that, despite the lack of concrete evidence for a drug-crime link, the established approach is partly based on the argument that there is such a link? One reason is that institutions and policies once in place are difficult to change, the probably more important reason however is that drugs are essentially criminalised for moral reasons. In the words of James Q. Wilson "drug use is wrong because it is immoral and it is immoral because it enslaves the mind and destroys the soul". Or for other reasons (political, cultural etc) that do not respond well to hard factual evidence.
Hans Durrer: A link between drugs and crime?