Tripped up by your ignorance again, huh?
Law enforcement officers’ duties are not set by the federal government. In fact, since the Supreme Court rulings applied to duties under the U.S. Constitution, it should be noted that the court’s rulings apply directly only to officers employed by the federal government.
The duties and responsibilities of a law enforcement officer are set by the state in which the officer is commissioned or licensed. The powers to define that duties of state, county, and municipal law enforcement officers are reserved to the fifty sovereign states by the Tenth Amendment.
Law enforcement officers are required to protect persons taken into custody because a.) they have assumed liability for the safety of that person and b.) because that person is generally restricted or confined in such a manner that they are unable to protect themselves. This precept goes back centuries in English common law and has been borne over into the U.S. legal system.
If you had any knowledge of the typical state penal or motor vehicle codes, you would know that police officers have no need to make up laws; there are already laws and ordinances covering practically every situation.
You chose to take an extremely small percentage of police interactions with citizens and make it a general rule. Yes, there are bad cops. But there are bad anything else, too. Bad doctors, bad lawyers, bad teachers, bad businesspersons, and bad parents. Sometimes people die because of their actions or inactions.
Furthermore, you choose to make blanket assumptions about the lawful use of force and deadly force by police officers in order to paint a completely false image and present it to support and excuse your own ignorance.
I would strongly suggest you do some actual research but why bother? You would much rather wallow in the cesspool of your own self-righteousness.