Unless you get rid of the factors causing the crimes in the first place locking up criminals just creates vacancies in the crime business. One lot of drug dealers is jailed, another bunch steps up and takes over. It's an aspect of a free market system.

If people don't think they are going to get caught, getting caught is not a deterrent. The same is true if they think they are going to get banged up whether they do anything or not, which is more or less where it is for a lot of people in some places.