There is no such thing as "American law". What counts here is how specifically state and local laws apply, especially for defense of persons and property. In the case of the state I reside in, deadly force cannot be legally used to protect property, except in the case of arson.
In light of the legal environment, the practical role of firearm is to allow a person to escape from the immediate vicinity of the threat. It is not much more than that, otherwise it is unlawful use of a weapon, assault, or one of the several classes of murder.
"practical role of firearm is to allow a person to escape from the immediate vicinity of the threat"
Not in Florida!!!
Thankfully, we are no longer required to flee from attackers, and are protected from civil lawsuit by the relatives of the Darwin Award recipient who got shot.