Thats the problem, where do you draw the line between rehabilitation and punishment? Getting criminals out of society is one benefit of prisons, but so is creating deterent to commit crimes. If I was a poor person and prison was this nice awesome place full of luxuries, I might actually want to go to prison. Obviously thats an extreme example, but how much of a cost getting caught is certainly plays a role when you ponder commiting a crime.

In ancient societies, they had barbaric punishments for criminals. The crime rate was high and they were rarely caught. And when resources are limited, providing someone free food and shelter is to costly and starving people might actually try to get in. Not to mention they didn't have any ways of rehabilitating people.

Personally I am in favor of more rehabilitation. There are alot of repeat offenders in jail, and most criminals are irrational and afffected by bias anyways, so trying treating them like rational agents doesn't work.

Before things go that far, shouldn't a society set up voluntary programs for treatment?

Who would volunteer to go to jail? Seriously, if the cops came to your door and told you that because your statistics suggested you were likely to commit a crime and you had to go to a "rehabilitation program", would you want to go, or resist (if possible)?

Exactly how does one draw the line between punishment and treatment?

From this, hypothetical, point of view, there is no difference. There is no real punishment, but you can hardly call sending someone to jail or worse, execution, treatment.

"consequentialists don't believe in punishment for its own sake, they do believe in punishment for the sake of, well, consequences."

I can't identify a single example other than Marxism in the last hundred years where the intellectual establishment has been very wrong

I'm reading The Rational Optimist at the moment which has a few examples.

Malthusian ideas about impending starvation or resource exhaustion due to population growth have been popular with intellectuals for a long time but particularly so in the last 100 years. Paul Ehrlich is a well known example. He famously lost his bet with economist Julian Simon on resource scarcity. His prediction in The Population Bomb in 1968 that India would never feed itself was proved wrong that same year. These ideas were generally widely held in intellectual circles (and still are) but there is a long track record of specific predictions relating to these theories that have proved wrong.

Another case that springs to mind: it looks increasingly likely that the mainstream advice on diet as embodied in things like the USDA food guide pyramid was deeply flawed. The dominant theory in the intellectual establishment regarding the relationship between fat, cholesterol and heart disease also looks pretty shaky in light of new research and evidence.

I'd also argue that the intellectual establishment over the latter half of the twentieth century has over emphasized the blank-slate / nurture side of the nature vs. nurture debate and neglected the evidence for a genetic basis to many human differences.