If it is just about money, stay out of it.
Problem is you don't know if it's "just about money" until after the BG has decided to be benevolent and leaves the scene without killing anyone.
There's many times that even after they get the money they still kill the clerk.
...
I can't imagine living with myself if I just stood there thinking "Oh its just about a few dollars" and watched some dirtbag kill some poor clerk.
I guess I also see the whole "I'm just going to protect me and mine to hell with everyone else" attitude as part of the reason this country is going to hell in a handbasket.
There's a bit of an oversimplification in this that is crucially important to recognize and deal with.
I used to hang out with some very smart folks who studied violent encounters in detail that most of us (even here) do not. One thing they harped on is an expansion of the old maxim that there are more tools in the toolbox than just a gun, or said another way "Just because you have a hammer doesn't mean every problem is a nail."
What does that entail? Social skills. Observation, awareness, empathy, comprehension, cues, tells, signals, predictions, first impressions, and all the other facets of human social interaction that we all (except for those deep into the autistic spectrum) exercise every minute of every conversation of every day.
No, until a violent actor has completely vacated the premises for good, we cannot say with 100% certainty what he will do. But that does not mean we are without the ability to make useful and necessary life-or-death analysis and predictions about what he wants, what he intends to do, and what end this narrative is heading toward.
Many folks have made statements in the past that us good folks just cannot understand or predict the behavior of criminals because they're crazy. Or because they just don't think like "normal" humans. Or because they're random, chaotic, or just evil. It is probably comforting to think that violent people and criminal actors exist on some other spectrum of behavior that is mutually exclusive with yours, but it isn't so.
If you are without a weapon, and find yourself in a negative and/or violent encounter, you will be straining every synapse to read the cues being given off by the bad guy (and the other good guys) to try to figure out your most likely path safely out of this situation.
With a gun in your holster, that should still be the case. You have one other potential set of paths to take -- that's the only difference. Having a gun with you does not mean that you can or should exercise the option to shoot (at) or threaten the perpetrator simply because you (claim, here on the 'net) can't possibly know what he will do next.
That's baloney, and hopefully not something that any of us would actually act on in real life.