Your fear is generally misplaced, here[0] are police misconduct stats (granted they don't count every single episode of police misconduct) and here[1] are crime stats. Certainly one episode of police misconduct is too much, but it's not nearly as high as crimes the police weren't involved in.
I think sites like HN and reddit showcase police misconduct and this leads to an exaggerated view of how prevalent it is compared to other dangers. It's similar to the MSM and sexual abuse/stranger danger.
[0]http://www.policemisconduct.net/2010-npmsrp-police-misconduc...