Their life experience is dealing with the disproportionately bad aspects of society, just like you probably have a disproportionately good existence. There are assumptions and biases that come from both these exposure models.
And maybe it’s just a problem with their delivery, but if you hear a political party (unfortunately the loudmouth fringe more often than not) incessantly talking about how you suck, should be presumed to be an evil murderer, and advocate policies that you feel put your daily safety at further risk, you might rethink your donations and voting history as well. Not defending the bad cultures and actors whatsoever, but there’s more room for nuance in discussing the issues we have policing this large, individualistic, culturally heterogenous, heavily medicated and critically unmedicated country. The problem is a hard one, so easy simple answers should be viewed with skepticism. There is no “just do what Norway does” answer to the problem that can be made in good faith.
I don't think that necessarily factually disqualifies anything I said already, though. The police are a necessary branch of the state monopoly on violence, but right now in the U.S. I don't think the demographics and tendencies of the police force line up with our collective expectations for transparency, honesty, trust, and justice. There are too many opportunities for intimidation and corruption that are taken and defended.
Edit: Also you're completely correct about one political party listening to and supporting the police.