The problem here is not the particular cop who threw the stun grenade in this particular raid. It looks like the cops did everything by the book. The problem is the damn book they were using, and ultimately that book was written by out irrational war on drugs that makes a social concern into criminal activity.
Hold on there, Ernest. Do not act for one second that the fact that the police have become a well-armed menace to good people has nothing to do with the type of people who are drawn to, and subsequently hired to be, police officers.
Be that as it may, it doesn't change the fault for that change into an overly armed, overly aggressive mode of policing is not primarily that of law enforcement, but of lawmakers.