Funny, I just saw this addressed the other day:
http://www.theagitator.com/2012/03/05/durham-loses-another-prosecutor/
Public choice theory tells us that public officials dont magically start behaving selflessly and altruistically simply because theyve chosen a career in public service. Theyll still act in their own interest most of the time, as we all do. Thats not an indictment of public service. Its a recognition of human nature, and how were hard-wired. In terms of policy, its prescribes that we design our institutions in a way that accounts for how people actually behave, not for an idealized version of how we hope theyll behave. The left tends to dismiss public choice theory outright. The right tends to believe its applicable to all areas of public service except law enforcement and criminal justice.