* They are delusional. They hallucinate guns. Not all of them, but enough to be alarming, simply are not interfacing with consensus reality. The things that are happening inside their heads are not the same as the things happening outside. This means that there is nothing a rational person can do to interact with these individuals safely, because the police aren't interacting with a rational person; they're interacting with a delusion. It is getting citizens hurt and killed.
* They create conspiracies. Even good people in a bad environment start influencing each other to do worse things. When several officers gang up on someone, they devise and support a story that may bear little or no resemblance to reality. This is visible in many cases where citizens or department cameras have recorded an event, only to discover that the audiovisual evidence differs greatly from the officer reports.
* Their background causes problems. The recruitment process is designed to attract people who feel comfortable with violent means of control, and court cases have ruled that it is legal to ban applicants above a certain intelligence level from serving as officers. The training at most academies then reinforces or creates patterns of thought which make people more suspicious and more violent, instead of focusing on facts. Better policies of recruitment and training do exist, but only in a few progressive departments -- who then enjoy dramatically lower rates of officer and citizen injuries along with much better community relations.
* They are above the law in the most literal way possible. They are not obligated to help anyone. They do not have to know the laws. They do not have to follow the laws. They can injure or kill citizens who are not breaking any laws. The chance of them getting punished for any of this is less than 1 in 1000. Since the main deterrent in law enforcement is not severity of punishment but probability of being caught, this creates a very attractive atmosphere for people who wish to harm others. This undermines the value of obedience and surrender, making suspects more unruly and putting officers at higher risk, because people naturally flee for their lives when confronted by violent attackers.
* In this specific case, notice the violation of medical neutrality. Health workers swear an oath to care for those in need; interference with this process therefore prevents them from carrying out their lawful duty. This is particularly disturbing given the prevalence of injured or ill citizens dying from lack of medical care while in custody. It also indicates that police are held to lower standards than soldiers and permitted to treat their captives worse than prisoners of war.
Why are we even paying these people? It's not law enforcement anymore. It's "Insurance," money paid to violent people in hopes they will hurt you less. But if once you have paid him the Dane-geld, you will never get rid of the Dane.
So, you don't have rights anymore. You have wishes. If they were rights, people would respect them or be promptly penalized for violating them. The police don't uphold the law anymore. If they did, they would be obligated to know it and follow it, or be promptly penalized for breaking it. These conditions are ruinous to the sustainability of a rational civilization. Naturally this upsets people.
A healthy society uses rational means to solve its problems. An ethical police force is thus representative of the population it protects and accountable to them. Here are some ways to stop police brutality, particularly in preventing more murdering people of color. This organization focuses on community efforts. The ACLU offers phone apps for citizens, as does CopBlock.
Quis custodiet ipsos custodes? We all watch the watchguard.