"Is there a difference between fire bombing cities & rounding up Jewish civilians & shooting them at the edge of a pit?"
A: Small difference. The father of my high school best friend served as a bombardier over Germany, and he was a quiet man, to put it kindly. His unwillingness to talk about it quelled some of my youthful enthusiasm for war.
Did a bit of research and paper writing many years later, that got me thinking about him. What a colossal, criminal waste of lives and treasure that was! British and American bomber forces suffered the highest casualties of any subset of Allied forces, and their true impact was not proportional. The old argument about destroying the Luftwaffe and diverting German resources to homeland air defense is weak. If we had let the cream of our manpower serve as leaders in the ground forces, rather than skimming them off to die in the bomber offensive; if we had turned that huge slice of our industrial capacity to bolstering the tactical air forces, building amphibious craft, and (perhaps) fielding better armor, we'd have been far more effective, far sooner, on the ground. That is to say, the opportunity cost for us was higher than the cost we imposed on Germany. The Luftwaffe would have come to the fight, and if that fight was over the battlefield and the interdiction corridors, we would have defeated them there.
The Oil Strategy in 1944 was the sole success of the entire 1942-45 campaign, and it came late in the game, because the strategists were fixated on the interwar theory that you could bomb a civilian population into submission (definitively proven false at the cost of a million or so lives), and the later belief that you could bomb industrial and military targets with sufficient precision to cripple them, at an acceptable cost. Both false premises. Our Brit allies were the worst - unwilling to accept the casualties of daylight "precision" bombing, they did all that they could do - area bombing of cities - with little effect other than the wholesale slaughter of civilians. And we learned from them and doubled down over Japan, where industry was strangled and the population already near starvation simply because of the air and submarine blockade of the home islands. But they were more the "Other" than the Germans had been, and it seemed
dulce et decorum to burn their cities because of the savagery of their rulers and their warrior culture.
So, yes, a national policy of extermination of sub-populations under the government's control (your SS shooting Jews into the ditch) was significantly different and worse than what we did; but we should have known better, and behaved better. The victors write the history; and brave men followed orders and earned honor thereby; but we should be honest about it.