We have been told for too long already that forbidding something will be the best way to make it stop from happening. That is just lies, especially when dealing with such addicting things like drugs.
People who have at some point become addicts, will do whatever is in their hands to obtein drugs. Whether it's legal or not.
The difference however is in the fact that an illegal product will very likely lack of health measurements and will provoke more anxiety on them, for getting it is more difficult.
By making them leagal, their levels of anxiety will drop and that's something that will be very useful by the time of a detoxification.
RE: Drug War Stories: Grief in Granger, Philosophy of Intervention Fails To Protect Us All