No doubt Beck was as well. And frankly, I think a reasonable person in his situation would have done likewise.
The vast majority of people have an aversion to killing others without provocation. Even the vast majority of robbers, who have no qualm about threatening others with death, have an aversion to actually killing their victims. Logan clearly demonstrated that he had none. Indeed, Logan had demonstrated that he had no qualms about killing even an entirely-cooperative victim; he was thus far more dangerous than a typical robber, as Beck was keenly aware.
Although it is quite plausible that, had it not been for Beck's earlier shots, Logan would have chosen someone else to be his next victim, I can't see that he's in any way to blame for his chosing Ms. Denmark. After all, if I inadvisedly take a 'hit' at a blackjack table and get a card that would have benefitted the next player, am I at fault for that person losing?
As another hypothetical, suppose that you are standing outside a restaurant and see that someone has lined up fifty people against the wall and is shooting one every few seconds. The shooter is between you and the innocent people. What do you do?
If you shoot at the murderer, you'll risk hitting one of the innocent people lined up against the wall. But every few seconds you tarry another of his victims will get shot. Do you wait until you can get a clear shot without anyone else in front of or behind the shooter, or do you say a quick prayer, take aim, and try for the best?
The fact of the matter is that while the notion of "first, do no harm" is often a good principle to live by, one who obeyed it slavishly would often be paralyzed. Like it or not, doing good sometimes requires risking doing harm because risk of harm is not always avoidable.
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.
Choosing not to fire means he would not have shot the woman. He doesn't know what would happen later and it's not his right to shoot at the woman, because of that.