Um...it's not at all and your associate is a fucking moron? If we get in a verbal argument and you punch me you have escalated violence. If I punch you back I have met it proportionately. Everyone kinda gets that unless you're really fucking retarded. What people get all stupid and dicey around, is in same situation is if after I punch you back you pull out a knife and attempt to stab me you have again escalated violence. But on the other hand if in response to your knife I take out a gun and shoot you many people will say I in turn also escalted. Nope, because it's proportionality to capability and intent. When we were both just punching each other (assuming we're talking bar fight style and nothing crazy) no reasonable person thinks the intent or capability of either of us is much beyond a some bruises and bruised egos. Once you tried to stab me you showed both intent to cause life threatening injury and capability by having the knife. I don't have to wait to actually be stabbed and bleed out to defend myself, I can shoot you. If an active gunman has shown capability and intent in any circumstance, and lethal response is warranted.