The concept of punishment is philosophically immoral and should be replaced with a more pragmatic philosophy of protection and prevention. We are endlessly complex creatures. We live endlessly complex lives. No two of us share the exact same experiences. This unique set of circumstances makes us unfathomable to each other. We are not Gods. We are only human and limited in our scope. As such no human being is qualified to pass moral judgement upon another. Therefore moral judgments should be replaced with pragmatic judgments.
Society should continue to isolate criminals and prevent them from harming others. But instead of saying "we judge you to be evil and will punish you to satisfy our desire for revenge" the message would instead be "We cannot hope to understand the complexity of you, nor of the events in your life which lead you to behave in this way. However, we have a duty to protect the larger society. Therefore we must isolate you from doing harm. We won't subject you to needless suffering. We pass no moral judgement. We will do what we can within the limitations of our resources to assist you in reform." Parents are responsible for teaching children right from wrong. Once they become adult it is too late. Society should not take on this role.
What would a society undertaking such a philosophical change be like? On the surface it would look pretty much the same. Criminals would still be sequestered. But on a deeper level it would be radically different. It could lead to some potential offenders voluntarily turning themselves instead of doing the crime. More importantly it would establish a more civilized, adult to adult relationship between the offender and society. This more grown up and humane relationship would likely create an environment more conducive to reform.