As a police executive in two agencies over a 42 year period I interviewed and hired many, and disciplined, commended, and fired a few officers.
I can tell you without a doubt that recruitment, selection, training, and discipline determine the quality of police service in your community. In response to Keystone's remark on numbers above, I agree that there are some individuals who want a badge for power and ego or other inappropriate motivations. Professional organizations understand that proper recruitment and selection weeds out most of those unsuited for police work, but now and again one slips through. Most of those who slip through the screening process are eliminated during field training or during their probationary period. Even then a few mistakes will be made but when you look at the millions upon millions of citizen contacts those officers have every year, the number of negative experiences is infinitesimally small. In my experience the number of officers who are honorable and honest in service to the community far exceeds the 95% number.
Professional law enforcement is expensive. If you want to hire college educated and/or experienced officers in a competitive job market, pay scales and benefits must be competitive. To have a robust recruitment program, investment in time and travel is necessary. Proper screening of applicants involving multiple applicant board interviews and psychological screening costs money and manpower. Law Enforcement agency accreditation, which requires the agency to adhere to a rigid set of professional standards, is manpower intensive and does not allow for cut corners in any aspect of policing, from hiring practices to staffing to training to complaint investigation to discipline. And you cannot overlook or neglect your dispatchers. The first contact a citizen has when calling for service is the dispatcher, and they often determine the quality of information the officers have to act upon.
Now here lies a conundrum. There are about 17,000 law enforcement agencies in the U.S., ranging from primitive to highly professional. Many agencies do not have the funding or resources or sophistication to meet the bar of professionalization. If you do not fund and staff to front-load your hiring process and do not maintain professional standards, you are going to be disappointed with your police service. Leadership and funding drive the standards. Your experience with law enforcement depends on where you are in large part. This is why I have always said that every community gets precisely the quality of police service that they deserve.
that feel as soon as they put on the badge they are better then those who pay their salaries. 
