It’s true that criminals become more criminals, while in prison because of the punishments they have. Neither an improvement found in them or any changing as well. We can also punish them in such a mechanism that they avoid to commit crime anymore. Like, by hiring them for jobs, giving them a chance to be a better human being.
As I believe, prison is a suitable place for criminals because there are proper environment and control system to deal with them. In addition, there are many activities they perform in prison to make them good citizens like ethical classes, exercise, and voluntarily works for the Police and security agencies.