[bsder]

What is the purpose of "prison"?

Sure, you need to keep someone who murders people away from the general population. That purpose of prison is restriction.

However, you have way more people in "prison" for things like drug possession. The purpose of prison in that case should be rehabilitation. You can help people kick their drug problem as well as gain education that they likely missed for various reasons. "Restricting" these people's access to resources is counterproductive.

The problem is that people in the US have forgotten that the purpose of incarceration should be about "paying your debt to society" and that afterward you should be reintegrated.

It's also an issue that people in the US seem to believe that prison has a deterrent effect. By and large, it does not (white collar crime being the exception--but we never hear about increasing the penalties for executives). People who are committing crime are not going to be deterred by small adjustments to prison sentences. They know that going to prison is a risk and are doing it anyway.