I’ve heard ideas that prisons could be voluntary in a completely free society. First, a lot of people who have gone to prison for victimless crimes (using and/or selling drugs for instance) would no longer go to prison. Second, people who have committed violent crimes may choose to go to prison to “work off their debt” and show willingness to atone for their crimes. One could imagine that many employers, businesses and people generally would ostracize a person that would not be willing to go to prison, but on the other hand would be more willing to again accept that individual if he did go to prison.

Have you seen the Norwegian system - https://www.businessinsider.com.au/why-norways-prison-system...

If it was nonviolent crime, then island where convicted can live with shops, houses, internet, trains and parks and local elected administration and cctv, but cannot go back to the rest of the world.

But if it is a serious violent crime, it should still be prison. Comfortable like in Europe or better, but preventing convicted from doing harm to others.

It should not be a punishment. It should be just an isolation. Separation of bad people from good people.

A lot of the times we would just do nothing. Marijuana possession doesn't need punishment for example.

Otherwise there are a tonne of options from before prison became the norm. Community service, restitution, fines, public shaming, exile, corporal punishment, capital punishment. Some more acceptable today than others.