Most petty crime is drug/alcohol related though - including muggings. Most drug users are driven by needing money, and its a constant need and a hard one to get round...
A friend is a nurse in a (male) prison and most of the inmates are addicted, some come in without adrug problem and develop one while they are in there
It makes me sad that they can't see any more than life in prison - that three meals a day and bed is enough