The military is a broadsword, not a scalpel.
Military-scale violence cannot be done in half-measures -- one should only draw one's sword if he's going to use it, and then one is committed, forget all bullshit so-called "rules" -- fight to win and utterly crush and humiliate the enemy. In this sense, laws of war are counterproductive; it lowers the threshold of organised violence way too far, and we end up with a long list of pointless scuffles and police actions, and with a lot of the backwards parts of the world just hating us.
(Laws of war were invented by fucking-idiot country gentlemen in 1945, when we had just come out of a no-holds-barred mechanized, industrialized war, and it was disciplined Western armies fighting disciplined Western armies. The fact is, many of the people we fight, fight like animals, and they do not fight Marquis of Queensbury Rules...) These men were not men of vision -- they were fools who just like Versailles, sowed the seeds of future conflict.
If I were president of the world, we would have not gone into Iraq or even Afghanistan, but I certainly would have had IS cut to pieces, if they existed. Thanks to 9/11, we have the perverse situation where the Americans invaded Afghanistan and Iraq, riled up the Muslim world; yet we now can't act decisively against the biggest bunch of fascists since the Nazis.
I think we have something to learn from the Russians in this sense. They understand these aspects of using organised violence way better than the West does. I would be comparing notes with them -- they have good experience of losing, then winning spectacularly against Islamist opponents.
If you're going to have blood on your hands -- it'd better be for a damned good reason. I wish our so-called leaders would think way harder before resorting to force. There IS a time and place for force (human nature being the way it is), but it's getting used way too often.