Police officers are supposed to enforce the laws. They are not the laws. Just because they have a badge and a gun, it does not mean they can act otherwise with impunity.
From Rodney King to Michael Brown, from Ferguson Missouri, to Baltimore Maryland, racism and abuse exist in police departments across the country. And the “reality of police abuse is not limited to a number of “very small incidents” that have impacted black people nationwide, but generations of experienced and witnessed abuse.”[source]
To assume all police officers are good is naive. After all, they are are human beings and subject to the same human frailty as all of us. But the difference is they have a gun and a badge and have sworn to serve and protect. Under stress, they make mistakes. And the results could be fatal.
Accountability demands reform. Not to mention those bad cops who knowingly abuse their authorities. Thanks to the prevalence of cell phone cameras, plenty of such examples exist online, just google “police brutality.”