Just a couple more comments on the humanitarian use of the A-bomb on Japan:
Hiroshima was only the 2nd - ever - detonation of an a-bomb. Nagasaki was the 3rd. No one fully understood the short- mid- and long-term consequences of such a weapon i.e. flash burns, radiation poisoning, cancers, deformed births, and so on.
Once these short- and mid- term horrors were realized, the powers that were decided that it was too ghastly to use again. And the bomb has yet to be used since (except for testing, and that is now banned world-wide). A very humanitarian outcome.
What if it was never used on Japan and the war ended. German was not far behind the US in the a-bomb development. Russia gained access to it. What if Russia, or Germany decided to attack the US with the bomb without complete understanding of the consequences? Then the US would attack the attacker .... ad nauseum. That alternate possiblity exists without the use of the bomb in Japan. Where is the humanity in that?
Now, on the firebombing: When Tokyo was firebombed, people escaped to the river to flee the fire, only to be boiled to death! True story. In Dresden, two people were trying to escape down a street, holding hands, when one simply dissappeard - melted alive - because they were too close to the infurno. True story (from the BBC's World At War). In these firebombings the people who died did not blessedly do so from smoke inhalation, they burned alive.
War is not humane. Period.