Prison all throughout human history is a way to segregate bad people, from the good.I dont disaagree with you that way things are currently. I actually agree with you. But what that tells us is 2 things. 1st If someone goes to prison its most likely better for society to keep them there in its current form.
Second and more importantly our system is broken especially prisons and we need to fix that. No its not an easy answer and I havent the slightest clue where to even begin. But this is something we should be looking into. Prison was meant to reform and it doesnt. So what else can we do. Again if we cant trust them with a weapon how can we trust them to walk amongst us and our Wives and Children.
The term "reform" was created to make the compassionate feel better about putting bad people in a bad place, hoping some good will come from it.