OK, if a bad guy has a gun on you will you draw your weapon and kill him before he kills you? You obviously have zero knowledge of a pending attack on your person until the crime has been perpetrated. At that time, it is too late to unholster your piece.
Now if you shoot him in the back as he is leaving the scene of the crime you are a murderer ask the LEO's being tried for murder of perps when doing their jobs.
What good is a gun if it is not drawn until after the crime and threat has obviated?
Carrying a gun is futile in the defense of ones self. No reason to pull a weapon until one has been assaulted by then it is too late the crime is over.