Didn't have time to read all the post, but wanted to put my spin on it....
Given: Working together, following the rules is what keeps a society safe and organized.
Non-violent Incidental violations or ignorance can be trained... no prison necessary
Non-violent repeat offenses, need a harder hand slap to help shoe horn them into cooperating with the society... no prison necessary
Individuals of violent crime, serious theft, those crimes which seriously disrupt society can not be allowed to trash out safety and order for the many... bottom line... they can not be released back into society... solutions:
Prison, at the cost of the offenders families. Problem, do we let family-less criminals to starve? Would this make us less human?
Prison at the cost of many through taxes
Prison labor camps, not pretty, but has minimal impact to the society. This would work well for a percentage of criminals. This may also be an intermediate place before re-introducing the individual back into society. This option has potential.
Banishment. Problem, some other society has to deal with them. This may work for a small percentage of criminals and societies. Hard to keep said criminal from coming back. Not the best solution.
Banishment to an island. This allows them to feed themselves and not be a burden on another society. This option has potential for worst case criminals.
Capital punishment, least costly, last resort for a stressed society.