The “Rules of War” aren’t ways to make it harder to win a war. They are ways to make it easier to win a war. For instance, if someone surrenders you don’t shoot them. Why? Because if you always shoot prisoners, why would anyone surrender? You WANT the enemy soldiers to surrender, that’s the whole point of the war. You’re trying to make the other side give up and do what you want them to do.
War isn’t just killing and destroying for no reason. I mean, some people kill and destroy for no reason, sure. But killing and destroying for fun isn’t war. War is using violence to achieve some political, social or economic objective. Maybe you want your neighbor’s sheep. Maybe he doesn’t want you to take his sheep, and would rather take your sheep. Maybe you don’t just want his sheep, you want his pasture too. Or his home, or his daughters, or his labor. Or you want to stop him from trying that shit on you.
Maybe you’ll have to kill him and his buddies to achieve this goal. But trying to kill people is, you know, dangerous. So it’s even better if you threaten to kill him if he doesn’t surrender and then he surrenders.
The whole point of the rules of war is that usually the war isn’t going to end with one side winning, and everyone on the other side dead. They’re going to still be alive, and you’ve got to deal with them after the war. Take for example China wanting to annex Taiwan. What’s the point of annexing Taiwan if you have to kill everyone on Taiwan to get it? “Taiwan” isn’t just the land, it’s the people and infrastructure. You want to conquer them and make them work for you. Sure, you could kill them all and bulldoze the buildings, and turn the island into a nature preserve, or move your own people in. That sometimes happens. But generally the value of X acres of empty land isn’t very high compared to the cost of murdering everyone who lives there and destroying all their stuff. They don’t want to be murdered, and will try to kill and destroy your guys and your stuff while you’re exterminating them.
So take for example our war with Afghanistan. We could exterminate everyone who lives in Afghanistan, and that would end the threat posed by the Taliban. Is that what you’re proposing? No, I imagine you’re thinking of just killing the Taliban. Except who are they? Are there X Taliban in the country, and once we’ve killed all of them the war is over? Or does the number change? Can someone in a village decide to help the Taliban one day and help the Americans a different day? What makes them decide this? If we think they might one day help the Taliban should we just shoot them now? Will that make other villagers more likely to help us or more likely to help the Taliban?
The notion that a war is merely an exercise of piling up a bunch of people and weapons on one side of a sportsfield, and piling up the enemy’s people and weapons on the other side, and they fight until everyone on one side or the other is dead is extremely pernicious. Yeah, you don’t like fuzzy and possibly unattainable goals like winning hearts and minds and prefer concrete goals like shooting people. Except how do you know you’re shooting the right people?