If you wish to justify a policy that will plainly increase the harms associated with each individual act of drug use, by creating violent criminal gangs as distributors, driving the sale of contaminated black market drugs, blighting the careers of users caught by the police, criminalising 3 million people, and so on, then people will reasonably expect, as a trade-off, that you will also provide good quality evidence showing that your policy achieves its stated aim of reducing the overall numbers of people using drugs.
