Personally, I think "deterrence" has an incredibly awful success rate. I also think that, if prisons should even exist, they should only be for physically dangerous people. Never for "money" crimes. Being locked away from society for years, your life destroyed and likely abused or even raped seems beyond "cruel and unusual" to me.

Personally I think the whole concept of prison is primitive and should be done away with. If someone is violent then they have something wrong in their head and should be treated. I know that currently asylums can be worse places than even prisons, but once we move away from this draconian "people must suffer so I can feel better about wrong in the world" strategy we can move much more focus on getting treatment and detection right.