I was contrasting that the war crimes committed by the Japanese military in Nanking have no nexus to the US military developing war plans to firebomb Japanese cities.
On the contrary: There was indeed a (moral) "nexus."
The legitimacy of the U.S. employing fire-bombing / developing and later using the A-Bomb was founded - partly - on the barbarity with which the Nazis and the Japanese waged war / committed genocide (and in part it was, paradoxically, also simply the most-compassionate means of quickly ending the war).
When dealing with so ruthless an adversary, ruthless means are justified.
Regards,