I found this in Quaker Faith and Practice, and thought it was worth sharing:
Imprisonment … offers some protection to society by removing the offender. But consider how limited that protection is compared to what it could be. It puts the offender against property into a place where he is deprived of opportunities to practise the social rules about property; it puts the violent man into a subculture which is governed by violence; it puts the defrauder into a power system where corruption is rife; it puts the sexual offender into a place where sexual relief is only obtainable by substitutes; … it puts those who need to learn to take control of their lives into a situation where all significant choices are made for them; and it puts the offender who is likely to reform into a milieu where most of the influences on him or her are criminal ones.
John Lampen, 1987