When we imprison individuals, we are putting convicts together and treating them like they are lesser beings. They grow resentment towards authority and society as a whole--they blame society for putting them away to rot. There have been studies proving that giving prisoners life skills reduces their likelihood of recidivism and increases their likelihood to become a valuable member of society. Drug addicts, on the other hand, should receive therapy. Drugs can be, and are, accessed in prison. Drug use can actually get worse, and as soon as they are released, they will more than likely go do more drugs. Getting clean isn't easy, and it is quite painful for an individual because their brain no longer produces necessary neurotransmitters due to chemical dependence. They need support more than anything.
Why do we have laws? It is to deter those who may commit a crime and then punish them if they do. Now if we 'cure' them more than we punish, we are only opening are pathway to more crime as criminals will have less reason to not commit a crime as the most punishment they receive will be check-ups on a psychologist. The fact is, we need to increase the punishment criminals receive so that they will not commit crimes. For example, change the 30 years for rape to the death penalty, and people are more likely to be deterred from wanting to rape.