I know people who have been in that situation in war, and @Dawn is right about that being the ones that haunt you.
And I think we do have to think this through, because when the bullets are flying its too late, the thinking it through time may kill you and others.
Some people may think its cold, but I have to compare it this way… consider a 9 yr old firing into a crowd.
Option one is I don’t shoot to stop the threat because they are a child… how many people die? What if its me? What if it’s not me?
Option two is I do shoot to stop the threat despite their being a child… how many people die? What if its me? What if it’s not me?
My right to protect my own life and the life of innocents is not trumped by the shooter being a child. If lives are going to be lost, there are still choices to be made. One child’s life against the lives they are taking. It’s a hard, cold math, but I know how it totals out for me.
Having done that math in advance, I hope, would help me make the best choice in the moment. Having done that math in advance is not going to mitigate all the emotional consequences, no matter what choice I would actually make.
I pray never to have to make that choice.