Police culture in the United States is routinely authoritarian to the point of brutality. Police officers swim in a culture of disrespect and hostility. Treating citizens with authoritarian rudeness outside of legal bounds is the rule and not the exception.
Mix racism into that, and you end up with an explosive combination.
If you are interested into looking into this further, Audit the Audit is a valuable resource on YouTube. The channel collects videos of police interactions with citizens, analyzing them in terms of legality and public policy.
The end result is not a pretty picture. The inescapable conclusion is that police culture in the United States is toxic and dysfunctional for everyone — but especially for Black people, other people of color, and poor people.