The reality is, most defensive gun use doesn't end with anyone being killed
https://en.wikipedia.org/wiki/Defensive_gun_use
Nearly a million defensive gun uses per year (if you go with the middle estimate).
How many end in "justifiable homicide"?: Somewhere between 250 and 300 (according to violence policy center).
That would mean that the overwhelming majority of cases are scenarios where the bad guy initiates and attack...potential victim draw weapon, bad guy decides "yeah, I think I'm gonna bail on this plan and live to fight another day".
In those cases, the gun has served it's purpose very well and didn't take any lives. Part of the effectiveness of the gun is that fact that most bad guys are afraid of it. If a bad guy pulls a knife or a baseball bat on me and says "give me your money", I like knowing that I have something that will make him think twice about that proposition and that will put me back in a position of physical advantage.