Downside of all this is that, if you are being attacked, and are alone, and return fire against more than one individual, chances are, your survival situation wont last too long.
Dont get me wrong; I am a gun-toting American, but I believe responsibility is the key here. Shooting (or ANY violence, for that matter) someone should be done AS A LAST RESORT. You are the one who has to live with your concience for the rest of your life; personally, I would have a hard time drawing down on someone unless the circumstances were pretty dire. I think that, with your post, you are thinking WWIII scenario. Chances are, if that happens, most civilians, and probably most everyone else, will be pretty much wiped out.
KAtrina was an excellent example of this. There were rampant shootings, violence, and general chaos. This included law enforcement personnel. Ask yourself; what do you benefit by remaining in the area? Some jamoke will likely plug you in the back. You walk around with your iron visible, acting all tough-guy, chances are someone's gonna take you up on it. And, in all likelihood, they wont be alone.
In a disaster area, where law and order is temporarily suspended, your best bet is to hunker down, with others if feasible, and wait it out. Personal defense is fine; just dont be shooting every yahoo who comes through your door. Eventually, order will be restored, and I guarantee you will be held responsible for your actions.