I do not see the use of the atomic bomb in WW2 as involving any sense of vengeance.
I doubt that President Wilson leaped with joy about the opportunity to kill a million Japanese... I have no doubt that we would have dropped one on Berlin and I would have no qualms defending President Wilson's decision to do so.
I wouldn't expect that 'President Wilson' would have leapt for joy, either -- considering that Japan wasn't one of the Central Powers during his WW1 presidency; neither did Truman (FDR's WW2 successor) do so and, in fact, we may have dropped them sooner had he thought it such a thrill.
As to 'vengeance' -- that was my point; I've had others call it that (and war in general, for that matter). One has been able to join the U.S. military as a 'conscientious objector' and, thereby, utilized in a 'non-combat' role. I could not "conscientiously" do so because, although I may refuse to go off on a killing spree just because someone like Himmler orders it (howbeit, that is much, much easier said than applied; almost as bad -- he had my 2 initials... UUUUGGHHHH!), I can counterattack, even for someone else's cause.
Not every German was a Nazi nor every Nazi a murderer or rapist; these things happened to the German citizenry when finally invaded. The major excuse was that "they did it to us" but the ones who became the victims were most often not the perpetrators.