There's a difference between criticizing rage police and advocating killing them.
If ione is criticizing them rationally, honestly and substantively about how they conduct their business, those people should be engaged by the leadership of the various departments across the country. That can be constructive. It can help build cooperation and trust.
If one is calling for killing police officers or committing other violent acts and just roiling up militant types, they should be watched and surveilled. Those people aren't trying to build trust and cooperation. Police can't use that though as a justification to suspect everyone is in that camp.