Speaking as an avid fruit preserver, I wish someone could explain to people like Bill Barr what the Bad Apples metaphor means. Having a few bad apples in the barrel isn’t about exceptions to the rule, a few bad apples spoil the whole barrel. When you have a few bad apples in the barrel, that is a systemic problem.
Police brutality is a case where problems of racism at the level of individual bigotry or prejudice constitute the root of more systemic racism. Having just a few brutal or racist cops on the force will break down trust between communities of color and law enforcement. Once that trust is spoiled, the police are not in a position to effectively protect and serve. Now you have a systemic problem. Everyone understands that the police must sometimes use force. But unnecessary brutality directed towards members of the black community will marginalize the entire community in terms of protection under the law. Given the history of violence against black people in this country, and given the history of violence against black people condoned or perpetrated by the police in particular, zero tolerance of police brutality will be a bellwether of racial justice in law enforcement at the systemic level.