No, I don't think you do understand. You are allowed to sit and have a moral opinion inside of a civilized society. It's because that civil order was forged with blood. And I don't mean that metaphorically. You live in a safe bubble because that bubble of safety was carved out by the hands of another. Because you live in safety, you have a false view of what the world is.
You don't call the lion a murderer when it's fighting off and killing hyenas.
There is no civility on a battlefield. There's only one rule and that is power. This is exactly what Jason Lowry discusses in his book Soft war.
Murder is a term reserved for civil crimes. Not for war.