You are misquoting or you don't understand what the standards of of deadly force is. You lack a legal understanding of the law. Police officer's do not have a license to kill. I have explained in an earlier post, police in a deadly force situation will use a gun to stop a suspect. They shoot to stop.
Reasonable force is the amount of force that a reasonable person would use under similar circumstances. For example, if an officer is attempting to arrest an unarmed suspect who refuses to physically comply, it may be considered reasonable for the officer to use a taser or pepper spray to force the suspect into compliance.
One of the obvious problems created by a reasonableness standard is determining the appropriate level of reasonableness. I can only guess that reasonableness is a mental state, what the officer believes is reasonable at any given time.
Police may use only that force which is both reasonable and necessary to effect an arrest there are three circumstances when an officer can use deadly force: first, when the officer is threatened with a deadly weapon; second, when the officer has probable cause to believe that the suspect poses a threat of serious physical harm or death to the officer or to another; third, when the officer has probable cause to believe that the suspect has committed a crime involving threatened or actual serious physical harm or death to another person.