Uhh, that's my point.
For someone whose only crime is using, or perhaps selling, illegal drugs, do you really think that incarceration is a benefit in learning to become a good citizen?
First of all, it does serve as a deterrent. Most people don't want to go to jail. Secondly, if you are suggesting that incarceration can't be a benefit in learning to become a good citizen (i.e, stay out of trouble - stay out of jail), then I guess your argument is that only people with life sentences should be serving time.
I disagree. Going to jail, even if for only a short period, is the best thing that could ever happen to someone headed in the wrong direction.