It is a mechanism of punishment. This depends on the jurisdiction. Prisons serve many apparent purposes, the mix of claimed and actual intents varies: punishme

It is a mechanism of punishment. This depends on the jurisdiction. Prisons serve many apparent purposes, the mix of claimed and actual intents varies: punishment, deterrent, removal from society for society's protection, commercial reasons, reformation, historical precedent ... Whatever, I agree that few jurisdictions do a great job of lowering recidivism, putting into place the societal structures to support ex convicts after release in finding stable work and so on.