The bias is justified. When you commit a crime, it is this single worst action that you are judged for, ignoring any positive contributions you have made. So

The bias is justified. When you commit a crime, it is this single worst action that you are judged for, ignoring any positive contributions you have made. So judging cops based only on their worst behavior is quite valid, especially given the power they wield (which seems to include the power to be judge, jury, and executioner).