> Saying "He had no free will" doesn't mean "The state has no right to confine him away from people he might hurt."

You get it.

Saying "he had no free will" would mean there's no basis for using incarceration for vengeance, and it ought to change how prisoners are treated. It does not take away a legitimate need to lock people who remain a threat away. Nor does it entirely take away a justification for some use of incarceration as deterrent, to the limited extent it actually works.

It just means a different calculation over how and when the harm done to those incarcerated outweigh the risks and harms to society of letting them go free, as well as a collective responsibility of society for addressing the conditions that causes these outcomes in the first place.