The shock is not only that a police officer killed an unarmed black teenager. That, tragically, has happened too many times before, and when the details remain murky, many people withhold judgment. The shock was that the police response to the protests was so hugely disproportionate, "like an invading army."
The military mission is to confront and kill a defined enemy. The peace officer has no enemies. His or her mission is to protect the community and everyone within it. No matter what crime they may have committed, all are entitled to the protections of the Constitution, the Bill of Rights and due process.