Some are not emotionally stable enough to legally have the power to carry a loaded gun and use it to kill/shoot/murder someone.
There should be a test for that too. So far all the cops in the news who hipshoot black men to death are terrified. Now that should be a nobrainer indication that the requirements for being a cop are either not known and enforced or known and ignored. How does that work for you? It sure doesn't work for me.