I'm not sure that someone will all of a sudden snort cocaine based on the fact that it's legal. If you were doing blow off a hookers ass before it was legal, chances are you'll do the same after.
Portugal is an excellent example of how most drugs were decriminalized and the approach was to help users rather than incarcerate them.
PS: This thread may have gotten off topic but this is the real discussion we should all be having as it is the root cause of these kinds of incidents.