OK..we agree to disagree, but I happen to think that when a thug attacks a law officer..he is taking a chance on being zeroed out...and rightly so !
Perhaps they risk that but NOT rightly so. You or I if we killed a person who had only cold cocked us would go to prison for the rest of our life. You can shoot ONLY if you are in mortal danger.
Now iffen Mr. Badguy doesn't just punch the cop but is on them and beating the life from them then yes they can kill or more technically can shoot to stop their actions. Once the action stops so must the shooting.
You are letting emotion get in the way of reality.