I think more core to the issue is status quo bias. Cops are much more likely to agree or strongly agree to questions like “the current US system is fair and just” and similar pro-status quo ideas. Typically speaking left wing protestors are agitating to change the system, especially policing, which is why cops do not respond as well. Is it any surprise that cops respond worse to those protesting against the police, no matter the slogan, than they do against the “blue lives matter” crowd?

Oh, and cop organizations are run through with neo-nazis and white supremacists who have made a concerted effort to make inroads with police departments and military members.