I think they are fully obliged to shoot or to obey orders to shoot once in action. Them not shooting can and does cause the death of fellow soilders. What would his faith tell him about causing the death of that soilder, he did not shoot him but his inaction would cause the death of another...
I look at it like this. You find a wallet with money, credit cards, etc. in it. There is also the contact information for the person who's wallet you have found. The devil is that little voice inside that says keep the money, trash the wallet. You think, No I will return the wallet. Then that...