Well, I disagree that some form of prison is necessary. Like I said earlier somewhere I'm here, my opinion is probably a very unpopular one. I believe that if we can create a set of laws with no victimless crimes (which are also barbaric) then the world would be better with 2 sets of punishments: fines and corporal punishment, so long as no maiming is allowed in corporal punishment. I believe such a system would be much less barbaric than any system based around incarceration, and I believe incarceration is ineffective as a deterrent, and as rehabilitation. As far as protecting society from the criminally inclined, you're basically saying some people must be removed from society, and I would agree on that, though I think not nearly as many as we think go into prison like that, but many more come out like that, and I can think of a more humane way to remove that element from society than locking them away for the rest of their days, if they're truly beyond rehabilitation.