A guy who deals dope to kids is a dirtbag that deserves to be put away. A guy who smokes a little ging to unwind is no more a criminal than someone that stops at the local pub to have a few pints. As a matter of fact the guy having a few pints and getting behind the wheel of a car is a far greater danger to society then the guy sitting at home smokin dope and watching Pink Floyd's "The Wall".
So if its really about protecting society, as criminal justice is supposed to be, shouldn't we be more focused on those people that engage in activity that actually is a threat?