Do you believe prison changes people for the better?

On one post I saw someone talking about how a certain sentence was enough time. Such and such time was enough to think about the crime this person committed and change. Personally, I thought this was hysterical especially for the way US prisons are set up. They don't really aim to rehabilitate. They aim to punish. I don't think their thoughts are trained on what they did, their thoughts are getting out and staying alive while in the slammer. I also think that people like rapists and murders typically don't feel sorry for what they've done.

Its also proven that nearly 50% of prisoners released, go back to prison within 3 years for new crimes or parole violations. I believe its higher for people who are released with no support and no resources to turn to.

So what are your thoughts? Do felons come put better, changed people?