It's not that simple. Guy points a gun at me, I shoot him, he dies. I'm not hurt. Was my use of force justified? Yep. Will I be in trouble? Nope. But, someone bumps me, and I jump up and hit 'em in the jaw, knocking them out? Yeah, probably in trouble. Or... someone hits me, then turns and runs away. I chase 'em down and shove their face into the mud. They're not hurt at all, just their dignity. I've got a bloody nose. But I still get charged with assault. Now, I'm oversimplifying these examples a bit -- but the principles are demonstrated.