Framing is a psychological principle thought of as a persuasive technique, though framing is much more influential in our own lives.  Framing changed conduct.

A police officers soldiers or protectors?  How a police officer views himself will determine whether innocent people live or die.  Espinosa v. San Francisco (CA9) (here) is a classic example of the cop-as-soldier frame:

Officer Alvis climbed into the attic with her gun drawn. Officers Morgado and Keesor entered the attic after Officer Alvis with their guns drawn as well. It was dark, but Officers Alvis and Morgado had flashlights. Officer Alvis shouted that she saw Sullivan. An officer responded over the radio “Hey,why don’t we just pull back really quick, set up a perimeter and just try to get him later.” Officer Alvis then shouted  “Cover both closets. I have him at gunpoint. He’s not going anywhere. . . .” 
No one was in Espinosa was in any danger.  The man police killed was not holding anyone hostage.  He was trapped in an attic - where he had been sleeping.  The police didn't even have a good reason to be in the man's apartment.

Painted on police cars is, "to protect and serve."  Whom were police protecting when they drew their guns on a sleeping man?  Whom were police serving when they shot an unarmed man?

Modern police forces have become militarized, as Radley Balko covers in detail here.  Police officers are not trained to protect and serve; they are trained to shoot first, and ask questions later.

In a military setting, collateral damage is recognized as justifiable.  Innocent people die to further the military mission.  Even in just wars, collateral damage is inevitable.  ("As tragic as it is, collateral damage to innocents is an inescapable consequence of war. Catholic theology recognizes this. It applies to such situations a well-established principle known as the law of double-effect. According to this law it is permissible to undertake an action which has two effects, one good and one evil, provided that certain conditions are met.")

What just war are police fighting on American soil?  Why has the police frame shifted from that of the beat cop who knows his neighborhood and interacts with the public, to armed-and-dangerous soldiers who illegal enter homes and shoot to kill?  

Whatever the cases, the effect is clear: Police do not view themselves as protectors and defenders.  Why then should we?