No, we put people into prison for several valid reasons, the best of which is that we hope that we can protect people who are on the outside.   We also hold out some (faint) hope that the prisoner will reform their ways, but for most of the population we just warehouse them hoping they'll grow up and too old to try those things again.

The GOP in Michigan promised in the Engler years to build as many prisons as it took to make places like Detroit safe again.  The GOP passed stiff sentencing laws -- some of which I disagree with -- which then filled these prisons.  In a few short years, Detroit ceased to be the murder and drug capitol of the nation.