And how exactly would you know that you just run into a mugging and therfore leave the gun at home before?
And would they wear uniforms and their goals would be clear, I'd say: everybody takes a rifle and then we clean the world from that s
. But the fact is: we don't recognize them and we don't know what exactly are they up to and whether they stop after minor teasing or want blood. I guess in most cases they don't know either. That is the grey zone. The assholes always have the advantage that they can strike first, as they are defined by their aggression. Of course one could kill them the moment the say "faggot" just to get sure nothing worse can happen. Every group has a dynamic and that dynamic can change events in every direction. Unless you can spot that early (which is absolutely possible in some cases and something good policemen are good at) you can recognize where it ends. People not trained for confrontation of that kind can not.
Of course there are clear cases like the one you described: someone pointing a gun at you after already attacking you is a damn obvious case of self-defence. But even in that situation - play through all the alternatives:
They hit you, you try to get your gun, they are faster and then shoot you with it, because, hahah, their gun did not work. Then they go on and use the gun on several occasions because they now have that nice spare gun they can throw away if they have used it enough.
They hit you, you draw your gun, and you shoot immediatly and end up knee-deep in dead bodies without knowing what the outcome would have been, hadn't you done anything.
You don't have time to grab the gun, everything happens as it happens, but the moment they flee, you shoot the fuckers in their backs. Which they deserved. But: did you deserve to be that person?
I am not saying that a weapon could not have helped, but the conditions are by far not as clear as you make them appear. Neither is that "felt" mistake of not arming yourself. There was injustice because the attackers wanted injustice to be there. Even killing them one by one would not have stopped the injustice, as you would have been forced to take the responsibility, if not in front of court, than at least in your own mind. This is why I refuse to believe that this can be an adequat solution.
I know, the feeling of being in control is nice, but in the end you are not in control as the aggressor dictates how the game moves on.