Things like that are common. When you have an unfair war, soldiers often make them fair in their minds by creating a set of rules that they can follow, which gives them a source of authority to justify their actions and transfer their own guilt to.
It's where the traditional codes of martial conduct, like Bushido and the Chivalric Code came from. They're both sets of rules that grew to encompass most of life, but originated from a set of generally-accepted rules as to what was fair in combat. It's funny, but most of the people who complain about how silly these codes are do it because it gives all sorts of advantages to the weaker party and the defeated and say that it's obvious that the losers need these up to avoid getting trampled. These people have completely missed the point. These codes are built for the winners, so that having killed people face-to-face, they can go home relatively free of trauma, the pain of having killed being eased by the knowledge that you followed the rules, and that the enemy knew the rules in advance before they came to fight.
It's interesting to see how this has changed with modern warfare. You have increasingly lopsided conflicts, with forces that have total numerical, strategic, intelligence, training, experience and hardware advantages against much weaker enemies, making war much less fair. You also have increasingly powerful weapons making civilians casualties far more likely and more numerous when they occur. However, you also have far less personal means of killing. Whereas in history when you killed a man you felt the shock in your arm and the resistance of flesh and bone as you cut through his chest, now mostly soldiers point a gun at someone else, press the trigger, and see a small pink mist and a man fall over, and even moreso, weapons where all you have to do is press a button and thousands die.