I don't think people who use drugs should be arrested, prosecuted or incarcerated. I'm pretty sure that statement alone will brand me as a liberal, but in reality it is conservative value I am espousing. Government, of which our police forces and judicial system are a part, have no place in forcing moral values on its citizenry.
Many people's distaste for recreational use of drugs colors their judgment in this area. They'll point to gang wars, robbery and all other sorts of mayhem to justify why as a society we should put drug users behind bars. Stealing, mugging and other such actions are illegal because they harm another person or persons. Drug use may or may not harm the user, but how can what a person does to themselves be illegal?
The purpose of laws is to protect citizens from one another's acts and actions. Law was never intended to punish people for making decisions and acting on those decisions that only involve themselves.
Let's take it one step further. America is growing obese at an epidemic rate. Suppose it became illegal to purchase and consume junk food? After all, junk food has little to no nutritional value and only adds to a person's likelihood of becoming overweight. Officer, arrest that Little Deb freak over there! Put him in the clinker and throw away the key!
It sounds far-fetched, doesn't it? But it's the same principle. It's just a matter of common sense.