The "Normal Rules of War" throughout history include the sack and rape and burning to the ground of entire cities with the inhabitants heads neatly stacked outside.

In the European Theater the targets the US 8th Air Force picked were generally targets of military value, like plane production or oil or ball-bearing plants. Most were placed in cities and bomb accuracy at the time was measured in miles. Other targets like railroad junctions, airfields, ports and bridges were usually in populated areas. Everyone just thinks it was "Target Berlin" when actually if you were at the briefing the target was actually the VKF ball-bearing plant at Erkner or the like. (not speaking about the British effort which done at night was more Target Berlin)
Even by 1944 the Germans were still producing over 3,000 combat planes a month. Do you do nothing to stop that and let them ramp up production instead? What if at 10,000 planes a month they can hold us off? In this kind of modern mechanized Total War the means of production are target #1. You can refuse to bomb them and instead have to kill 10 million German at the front in the planes and tanks you didn't bomb or plan B, you can kill a million in cities near strategic targets and 2 million at the front until they run out of planes and tanks and surrender with 7 million less dead Germans.
And with a draft inforced by the Gestapo you can't say the dead soldiers at the front were any more willing participants then the civilians back in the war plants.

Now the Pacific theater was a little different once LeMay took over, he just wanted to burn all the major japanese cities to the ground and pretty much did so. The Japanese had shifted production to cottage industry by then to decentralize production so the cities them selves had become the production centers. I think they should have stuck to strategic targets, killing civilians by accident is morally above killing them on purpose to me, even if the numbers are the same. I would have dropped the A-bomb on a fleet anchorage or large military base.