You're forgetting the cost of jailing them in the first place. Not only is there an upfront cost of $106k per year(assuming we're talking about CA)[1], that per

You're forgetting the cost of jailing them in the first place. Not only is there an upfront cost of $106k per year(assuming we're talking about CA)[1], that person is also not working(or paying taxes) or gaining any useful skills. What they're doing instead is hanging out in a population of other criminals and participating in a social order that incentivizes if not downright mandates behavior that in itself would be considered criminal in wider society. I don't think it's so far fetched to say that the cost society pays to incarcerate someone with the goal of preventing them from committing more crimes can exceed the cost of the crimes themselves. Deterrence is the only possible way to justify these costs(And prisons do have nonzero use as a deterrent), but the current prison situation makes it clear that prison's RoI growth has some seriously diminishing returns that started at a funding level far lower than the current one. [1]https://lao.ca.gov/policyareas/cj/6_cj_inmatecost https://lao.ca.gov/policyareas/cj/6_cj_inmatecost