If you want to exercise the right to keep, bear and use arms, then you must learn how to use it and accept the consequences of your actions.
Your examplw plainly gives the reality of what is. Psychics and the like need not give their opinions. Folks are being shot one by one. The outcome is clear and there's only one way to end it. Beck didn't have any such certainty in the outcomes of his 2 possible choices.
" I think a reasonable person in his situation would have done likewise."
Pondering possibilities is BS. When there's bystanders DON'T FIRE UNLESS YOU ARE ABSOLUTELY SURE! If you fire then suffer the consequences.
Snap? Snap is what happens when you here some clymer, that blasts your vehicle, you, or your kids full of holes say, it's because he's trying to save you, your family and the world from harm. I don't care what goes through his mind all I give a damn about is that he don't shoot at me. That includes cops. I don't appreciate it and no reasonable person would either. If you don't mind being plugged in a pray and spray for salvation, fine. I mind, because it's deadly recklessness.
In my example, it's not 100% clear what would happen if you do nothing. The bad guy's gun might have just run out of ammo, or it may be that the bad guy only wanted to kill certain people, the last of whom he just had.
What's important is not that someone will, with 100% certainty, be killed if you fail to act, but rather that the probabilistic expected harm to innocents from action is clearly lower than the probabilistic expected harm from inaction.
Suppose Mr. Beck were clairvoyant, and knew that if he did nothing, Mr. Logan would flip two coins and if they both came up heads he'd let Ms. Denmark go uninjured and otherwise he'd kill her [i.e. there was a 75% probability that she'd be killed if he failed to act]. Further, he was very precisely aware of his marksmanship skills and knew that if he shot at Logan there'd be a 25% chance of Ms. Denmark escaping uninjured, a 25% chance of her escaping with non-critical wounds, a 25% chance of her being shot fatally by him, and a 25% chance of her being killed by Mr. Logan [if he gets away with her, he won't bother with the coin flip].
Under such circumstances, should he shoot or not? To be sure, there'd be a chance (6.25%) that his action would kill her when she otherwise would have lived, and also a chance (again, 6.25%) that her actions would result in Mr. Logan killing her when he would otherwise not have done, but despite those risks her probability of survival would have been doubled. In chart form:
| Coin result |
Shot result | |||
| Escape uninjured | Escape injured | Killed by Beck | Killed by Logan | |
| TT | Much Better | Better | Same | Same |
| TH | Much Better | Better | Same | Same |
| HT | Much Better | Better | Same | Same |
| HH | Same | Worse | Much worse | Much worse |
Suppose Mr. Logan knew those precise probabilities. Should he act or not act?
Now you may very well posit that he could not have known any of those probabilities nearly as precisely as I am suggesting, but I think he would have been quite right in judging that Mr. Logan had a very high probability of killing an innocent person if not stopped (higher than the 75% cited here), and that the risk to Ms. Denmark of being hit by a stray bullet was less than the risk she would have faced had Logan not been stopped (he might reasonably have guessed them lower than cited here).
The fact is that Mr. Logan was in a situation where any course of action he could take had a very high probability of turning out wrong. While he chose the course of action that would be more likely to result in him being blamed, sometimes that's what courage is about. If he'd held off on a shot he thought he could probably make, for fear of shooting Ms. Denmark, and Logan then proceeded to kill her, I don't think anyone would blame Beck for holding off but he'd nonetheless probably blame himself--moreso if something happened to his family.
Whether or not Mr. Beck's judgement was perfect, I certainly do not think it unreasonable.