I would also note that while you've given evidence that breaking international rules regarding killing civilians can be useful, the question is whether or not the benefits outweigh the costs. How much shorter will the war be if you kill all the farmers? How many fewer men will die in total because you nuked that city? How much less will future generations value human life because rape and torture are considered acceptable means to an end?

My knee-jerk reaction is that having these standards may indeed reduce overall casualties and that they are important for international image and future cooperation. I am open to evidence to the contrary though.