One could also argue that there was an earlier failure(s) of the system if people reach the point of having to protest to feel like they're being heard. So the

One could also argue that there was an earlier failure(s) of the system if people reach the point of having to protest to feel like they're being heard. So the protestors already see the police as yet another force trying to silence them which definitely strains that relationship. I think the issue here is that the protestors don't want to talk to police; they want to talk to the political/legal/social people in power to listen to their complaints. So the police are seen like a 3rd-party summoned by the people in power to stop the protestors and the situation is worse when the protests are about the police itself.