Though the police force is obviously highly important, we shouldn't ignore the negative aspects of our criminal justice system. In order to make quotas, NYC police officers must issue lots more tickets, and arrest more people in order to meet higher and higher quotas. This often results in numerous stop and frisks, especially of minority group members. This is being parroted across the nation. This continuous higher standard (an unreachable standard, since crime is not as high as the standard is) negatively impacts citizens as well as law enforcement officers.
Yes, in the last 30 years police forces have made the decent in to the bottom of the barrel. Not to say that all police forces or members are bad, but some have given others bad names. When asked most people would comment that they have little to no confidence or trust in police.
One of the biggest complaints I see from people about our (meaning the USA as a whole) police force is, it's too "militarised" and they're going to use this militarisation to somehow oppress the very people they're hired to serve. Sure I can see that most cops are a more armed and with better training, but then again, the manners of violent criminals have evolved greatly as well. So I see it as necessary evolution to deal with an evolving problem (criminals) .