Great points. The only time you can resort to a lethal defense is when you feel your life and well being is threatened. It is up to you to take every step to disarm a stituation prior from it escalating to that situation.
Leaving a situation is the best defense. It is not cowardly at all to avoid such a confrontation. If you have to run, run, but get out of there. Make sure every escape route is exhausted before going into the red.
THis situation is very subjective. If you are alone, you have many more opportunities to you. If you are standing between an agressor and your family, then you may have to stand your ground while they retreat.
If you feel there is a danger of bodily harm or death to your family or yourself, you have the right to act accordingly including brandishing a weapon.
If you ever do brandish a weapon and the situation is defused, immediately call the police to report an incident. Make sure you are the first to call. The best defense in this kind of situation is a good offense.