Having seen this issue debated ad nausium I will contribute my two cents and then bow out. Dropping bombs on cities is a morally neutral act. Why….
1 Militaries exist to blow things up and kill people. It is easier to blow up and destroy fields, mines, factories, trucks, trains, boats and all the paraphernalia that creeps up and makes a war effort possible than it is to kill soldiers. Best way to defeat an opponent in war is to take away their ability to resist. Starving unarmed men do not make good fighters.
2 Power to sustain a military effort requires millions of able-bodied people working in the logistical train from mines and farm fields through processing factories and finishing plants to trucks, trains, and boats. All are legitimate military targets because at every step of the way there is someone or thing involved in getting the troops what they need to win.
3 Cities exist because that is where the work is. If there wasn’t work in the cities nobody would be there. In time of total war between nation states, that usually requires almost the entire force is directed to support the war effort. And that means the military and the civilians working at supporting the fighting. The logistical supply line runs from the front line, where large amounts of metal is being hurled at a very fast rate at somebodies son, all the way back to the mine and farm fields where the food and weapons of war start.
Nobody said it is pretty it is just the way it is. This whole romantic thing of differentiating between combat and non-combatants is hog wash in a modern state where virtually the entire adult population will be involved in the war effort either at the pointy end of the spear or making spear shafts and pointy ends.
Ergo to forthwith I say bombing a city is morally neutral unless you are just into the wiping out of the indigenous population.
Atom bombs just makes it easier.