Sure, throwing the book doesn't get you 100%. But am I supposed to believe that increasing the penalty for doing the wrong thing doesn't decrease the frequency of the wrong thing? Having everyone you know in your crime circle being in jail vs. roaming free certainly has an effect on your decisions to join/stay.
Probability of punishment seems to matter more than severity of punishment. This follows from economic and game theoretic models and is backed up by empirical studies.
It turns out that when your big worries are "not being able to afford rent and food" and then "getting shot", the difference between 5 years and 20 years in jail, or the difference between a 10% likelihood or 50% likelihood that you get caught don't really factor into the decision-making process.
Sure, throwing the book doesn't get you 100%. But am I supposed to believe that increasing the penalty for doing the wrong thing doesn't decrease the frequency of the wrong thing? Having everyone you know in your crime circle being in jail vs. roaming free certainly has an effect on your decisions to join/stay.