Crimes of dispassion
OK all you criminals out there, hands up if ...
When you were planning your last heist (english translation - robbery) or slaying (murder), how many of you thoroughly worked out your plan and then ran the risk / reward possibilities through a spreadsheet before deciding whether to go ahead, or try something less risky instead.
No-one? How odd. You'd think that with "the needle" on the table, there'd be some sort of rational assessment on whether to embark on a life of crime. Maybe, it's just that people who slide into such a career (and it does seem to be a career - greater job "security" than most employment opportunities offer) aren't great at controlling their impulses - or have an innate view that they won't get caught.
If that is the reason then it explains why, 150 years after prisons became "popular" as a way of dealing with criminals, we still have a crime problem. After all that time, you'd think that if chokey worked as a deterrent, the problem would have gone away by now. As it is, the only things that a custodial sentence (or a terminal one) achieves is to remove the unsuccessful (i.e. the ones who get caught) criminals from society for a period and also, as Chris W says to satisfy the victims' and society's demands for revenge - or "justice" as it's usually called.