I'd also add a multiplier for actual crimes committed while under the influence.

There are certain individuals in society that will dope themselves up and rob people for more money. These individuals must be caught, secured and treated (if possible). If you're arrested for a crime, you are tested. If you are convicted of a crime, and you tested positive, your sentence (not fine) is extended and you are put in drug treatment.

The majority of the population will not have any more problem with decriminalized (or even legal) drugs than they have with legal drugs such as alcohol.