a) Germany and Japan started their respective wars, with much worse atrocity records. And with aerial bombing of their own. Japan was already bombing Chongqing in 1938. And during the counterinvasion of some of the islands did things like arm a school, including providing grenades to the children so they could avoid capture.

b) The scale of WW2 is so wildly different from the present that people find it difficult to imagine. The firebombing of Tokyo caused more casualties than one of the nuclear weapons.

(Follow on point from a: the original sin of all war crimes is starting a war of choice in the first place. Which the current war with Iran definitely is.)