Where you lock people up.
Several possible reasons :
- prevent serial criminals criming again
Also, prison or prison-like systems have been used time and time again merely as a mentally-unintensive clearing house for less "desirable" demographics. Why deal with a problem when you can sweep it under a giant rug?
So should we see prisons as a useful solution to a common problem, or are they one of many "cheap" infrastructures that serve mainly as pointers to our failings as a society? Just as poorhouses were testament to an imbalance in equity, is an abundance of prisons testament to a major imbalance in, say, interpersonal upbringing? – GrahamLally
RobertXCringely points out that the prison system is reliably predicted to cause crime : http://www.pbs.org/cringely/pulpit/pulpit20040812.html
LiberalDemocrat punishment : http://politics.guardian.co.uk/libdems2004/story/0,14992,1310747,00.html