I agree that a bank bag is a terrible way to carry cash. I much prefer a lunch box or insulated lunch bag. The presumption is that it either contains, or had contain a sandwich and a Coke. You are less of a target with a lunch bag/box.
As for using deadly physical force, it all depends upon how it is told.
In New York, a dog is simple property. I cannot protect my dog with deadly physical force. So if someone attacks my dog with a baseball bat and I am armed, I am supposed to stand by and not use my gun.
But I can impose myself in the situation, then the story goes like this:
"I saw him attacking my dog. I got between him and my dog and then he raised the bat as to strike me. I shot him in self defense."
For a late night robbery:
"He demanded the money. I handed it to him. At that point, instead of fleeing the scene, he raised his gun/knife/club as to attack me. I shot him in self defense."
Of course all of this presumes that there are no other viable witnesses. And even if there are witnesses:
"He made a move towards his holstered gun. I was afraid for my life. I also drew my weapon. My draw was faster, I guess..."
I think all of this has to do with "presentation of facts" and how they are told to the police. I think it is good thinking to rehearse many scenarios so that you can provide a plausible, but not criminal, response to the investigating police.
And remember that Bernard Getz really got away with murder until he opened his mouth and started bragging.
Bernhard Goetz - Wikipedia, the free encyclopedia