“A ‘simple’ punch can be fatal” is misguided logic. The use of deadly force (in every state and under the model penal code) is based on a criterion of “reasonableness”. The reasonably prudent man standard asks the question was the harm LIKELY to cause death or serious bodily injury, not COULD it have. Anything could cause death. Punches to the face are EXTREMELY unlikely to cause serious injury or death, therefore are EXTREMELY unlikely to support a DGU . . .
If you disagree with the above, ask yourself how many fist fights you’ve ever seen or heard of, then ask yourself how many people died from those fights. We’re talking one in a million. You don’t use a firearm to prevent something that has a one in a million probability of killing you. That, by definition, is unreasonable. As such, it is outside the boundaries of justified self-defense.