Bad cops killing unarmed civilians do not invalidate all police officers or even the necessity of a police force. We hope they are not common, and we hope that the good cops would speak up about bad cops and work to eject those bad cops from the police force.
A deranged man who tried to kill his girlfriend, killed two cops, and then killed himself is no more representative of all men everywhere than bad cops are of all cops.
The difference seems to be that the vast, vast majority of people who are protesting bad cops are also vehemently denouncing anyone killing cops. We’d still like to see the good cops speak up about the bad cops who kill unarmed civilians and escape justice as meted by our courts of law.