What the justice systems of most nations is missing is the idea of banishment and exile. In city states you were rarely imprisoned - that was very expensive to do, and society had to then keep you alive while you were non-productive. You were often enslaved, to work off your debt to the society. You were often beaten, but not maimed, because you were less useful crippled. If your (perceived) crime was severe enough, you were often killed.

But then there was exile, where you may not warrant your own death or loss of freedom, but the society just doesn't want you around any more. This would apply to the robber barons of modern times, the scam artists and those that prey on the weak. But we simply don't have the ability to banish such people - there is no where to send them, you cannot just put them outside your borders and say never come back. Even without any intent for retribution prison is a necessary construct to isolate those too dangerous to participate in society from it, but some criminals aren't actually physically dangerous. They are only dangerous with power, authority, or an audience. You would traditionally just want to exile those kinds of criminals after taking their possessions to recompense their victims, but we have no real way to do that anymore. Even if you had somewhere to put many of these criminals, the world is too interconnected to stop them from committing more crimes against your citizens abroad. Its often hard to completely strip someone of their accrued power.

So either they walk free with paltry fines or maybe rarely destitution, or they end up in prison like Madoff when they are so grossly criminal you have to do something. The breadth of response to crime today is to take possessions, take freedom, or in barbaric countries like the US take life. The option to take citizenship or residency is no longer an option, which is a shame, because there are a lot of crimes that would be well suited for it.

What about someone who commits auto theft? Seems like isolation is actually overkill and more inhumane than other forms of punishment. 24/7 GPS monitoring should suffice to make sure he doesn't steal again. But you still need punishment, else the calculus for the would be criminal is heads I get a car, tails, I get caught, but nothing bad happens to me.

Isolation is a punishment though isn't it?

Then just lie, cheat, steal and kill until one reaches their goal. In a way, it seems clear cut punishment is more humane than medicating or isolating a criminal out of existence. Punishment tells the criminal "this is wrong" in clear terms. Anything else communicates "you are an animal without moral agency and we treat you as such." Consequently, unpunished criminals will act as animals instead of rational beings.