I firmly believe that, even if you could prove to Americans that treatment is more effective at reducing drug dependency than prison, and at a much reduced cost to taxpayers (I don't know if that's true, I'm just postulating here), we still wouldn't implement it because darnit, it's just not right.
Treatment over jail works, every single time. How do we know this? We can look at Portugal and their drug decriminalisation and see what 10 years have wrought. Out of control drug use? Nope. Rise in drug use? Nope. All the yammering of the drug warriors is for naught. A real world example puts them in their place. We could also look at what Great Britain was doing before Ronny Raygun amped up the drug war and talked Maggy Thatcher into joining his failure. They basically decriminalised heroin, made it easier to get and use under supervision with an eye to treatment. Their heroin addict numbers plummeted and people were kicking the monkey. Then the US did as it usually does and screwed up a program that worked. Addiction went back up and criminality rose. The drug war's a failure and the warriors and their supporters just can't face reality.
Ten Years After Decriminalization, Drug Abuse Down by Half in Portugal - Forbes