Well here in Florida they just pasted a law that if you feel that someone is coming at you and you think that you are in danger you are aloud to put you gun out and even shoot a warning shot. But if the danger is coming at you with a gun then things change real fast. The danger needs to know that they need to drop the gun or you will shoot.
You need to make sure that you are in danger and before shooting to make sure he or she has a weapon that will hurt or kill you if you do not take action.
In a SHTF where the law is no were to be found then you need to defend your self and your family.