Not going to help them out that much though, some cocaine addict may not be harming others, but he'll grow up and end up as someone useless to society and to himself.
When cops do need to intervene in your scenario, though, it's not going to be much different than now, they're still aiming to toss you in someplace. And that guy can still be a gangbanger in the cops eyes, or a mugger or some other kind of crook once being a druggie is out of the equation, and likewise the people will still distrust the police as much as they do now.
Perhaps in 50 years or so that might change though if they decided to change the stance on drugs, but I am doubtful such a utopia will present itself.