Police, through their unions, and individually, are citizens and individuals. They have the same rights as any other citizen to attempt to have input as to public policy, including educational policy.
I'm not a censorship guy, but I can understand why police officers and police departments would be concerned about an unbalanced presentation to students in public school as to the character of police officers. In a responsible, functional society, persons don't hesitate to call police when they witness a crime, or an accident, or believe themselves or another person to be in immediate danger. It is a dysfunctional society when persons will not do it, and it is a criminogenic society when peer pressure (at a minimum) is put on persons to convince them to NOT involve police in criminal investigation.
It's one thing to teach kids about the issues of racial inequities; it's another thing to present those realities as if Bull Conner is still alive and on the job. It's also another thing to educate children in a manner that they come to believe that police officers are the #1 source of lethality for people of color, but no mention is made of gang members, drug dealers, and other criminal elements who pose the greater danger to people of color in their literature and educational materials. This may be a bit of an exaggeration of the narrative distortion that is going on, but not much of one.
Brutal police need to be bounced, and criminally charged if their brutality rises to that level. But a police officer using deadly force is by no means not automatically a situation that did not justify deadly force just because the subject didn't have a firearm; that question depends on objective reasonableness and the totality of circumstances of a situation. Indeed, presenting to students what Courts have actually said on this subject, and what the concepts of "objective reasonableness" and "totality of circumstances" mean in real life. That would actually be providing students with an objective education in criminal justice if THAT were taught in schools.
Trust can be eroded though systematic campaigns to discredit one side by providing a stream of information that includes only one side of the argument. Of course SC teens will not trust police if these items on their reading list constitute their entire source of information on how the criminal justice system really works.
There are also many contributing to this particular narrative of how "the Police are the Enemy" and ask why they are taking this stance.
Is it because they are engaging in illegal activity themselves, and do not want to be discovered?
Is it because an immediate family member is engaging in illegal activity, and that family member's remaining at large is more important to them than the safety of the publc?
Is it because they are in a situation where the local culture is one where people are actively intimidated into not calling police, not offering their witness of crime to law enforcement, suffering silently when they, themselves are victims of crimes, because they are intimidated by active criminals in their own communities?
Is the "Racist Cops" line sometimes a cover for people who are ashamed to admit that remorseless criminals in their midst have intimidated them into silence?
Decades ago, when I was a substance abuse counselor, I was subpoeaned to Court on a client who failed to complete the program I worked in. Before his case was called, I was present for another sentencing; this one of a man who was selling cocaine. It was, based on the testimony of all, not his first time before the Court on issues such as this. His attorney asked for leniency, and his attorney, the defendant, and witnesses on behalf, testified of the tough neighborhood he came from, and the circumstances of life there. The prosecutor spoke last, and while conceding the circumstances this man grew up in, made the statement that this man was also a reason that the community he lived in had the problems it had, and that this man had did much to contribute to the ills of his community.
Life is full of competing narratives. The "Racist Cops" narratives certainly have truth to them; there are police officers who are racists who have slipped onto the force. But police brutality is not a solely white thing; indeed, the issue of Freddie Gray involved black and white officers working in a city dominated by African Americans. And the narrative of citizens intimidated by gangs and drug dealers also has truth to it. The narrative of citizens not wanting contact with police because they are dealing/possessing illegal drugs, or someone in their family is, has some truth to it. The narratives of "Racial Profiling" in everyday policing have some truth to them.
But there is a bottom line, and the bottom line is what separates a functional society from a dysfunctional society. And a society, ANY society, where persons are unwilling to call law enforcement to seek protection from criminals and are unwilling to offer themselves as witnesses against criminals, due either being intimindated or just resentful toward law enforcement, is a dysfunctional society that will not be able to protect its own members. Narratives that are exaggerated and distorted that serve to block cooperation with police are narratives that preserve dysfunction and maintain the unsafe status quo.
