How did imprisonment go from being seen as a key component of society's solution to social conflict, at the turn of the nineteenth century, to a practice that perpetuates and exacerbates that conflict?
In Discipline and Punish, Foucault puts it this way: "We are aware of all the inconveniences of prison, and that it is dangerous when it is not useless. And yet we cannot 'see' how to replace it. It is the detestable solution, which one seems unable to do without."
Why do we keep using it, when it is "dangerous when not useless "?
Well, as Foucault notes, two centuries ago, imprisonment was conceived not merely as the deprivation of liberty, but also as an occasion for the transformation of the offender. One can still observe this in the names of many corrections departments around the country; the institutional goal of correction is right there in name of the agency itself. (Nevada, with its Department of Prisons, is one notable exception.) The idea was to rehabilitate, not simply to incarcerate.
What is left of that idea now, a generation after the widely cited meta-analysis by Martinson and others asserted that "nothing works" in correctional programming? A "what works" literature struggles to find a proper hearing, amid all the budget cuts relentlessly eating away at rehabilitative programming. It's hard not to be a warehouse, if you don't have money to do much more than feed, house, and clothe (in jumpsuits) the inmates.