Mass murder is mass murder, regardless, but those who commit it will usually seek to justify it after the fact...while those who suffered its consequences (in a collective sense) will protest it and seek revenge, compensation, or at least recognition of their suffering.

The USA committed mass murder numerous times in World War II, as did most of the other combatants (Japan very notably included).

The USA naturally tries to whitewash its own actions in this regard, and was aided and abetted in doing so by being on the winning side...a very useful place to be when justifying war crimes.

It is entirely possible that Truman and his advisors thought they were doing what was best when they dropped those bombs.

It is also possible that they just wanted to test those bombs on a real target and couldn't resist taking advantage of the rapidly dwindling opportunities to do so (Japan was nearing economic collapse and military impotence...in fact had already pretty well reached military impotence in terms of being unable to launch any more offensive operations in the Pacific theatre).

It is also possible that they wanted to send a message to the Russians...or forestall a Russian advance into Japanese-occupied areas in China and Manchuria and Korea by ending the whole thing quickly before the Russians could get very far with that.

They were assuming an amphibious invasion of Japan in 1946 would cost a million or more lives...BUT no such invasion would, in fact, have been necessary in order to secure an end to the fighting. So their assumption was based on somewhat unimaginative thinking, based on the war in Europe.

They were demanding unconditional surrender...but it is never necessary to demand unconditional surrender in order to end a war...and NO surrender is in fact unconditional, truth be told! (Unless everyone on the losing side is dead.) There are always conditions.

It's a very twisted tale.

Those who are emotionally committed solidly to either side of this debate will naturally simply reject out of hand any opinion which opposes their own.

Therefore, I shrug. It's all been said over and over again anyway.

I suspect, sadly, that if the atomic bomb had not been used on Japan in 1945 it would soon have been used somewhere else...against either Russia or China...and that would have been potentially far more catastrophic for the World. So, maybe we all got lucky...with the exception, of course, of the incinerated and irradiated Japanese citizens in Hiroshima and Nagasaki. They were most unlucky, and served as the sacrificial lambs on behalf of the rest of humanity...who stepped back and took a second look at the Frankenstein monster that their clever scientists had brought into the World.

It's the sort of thing you can get away with...until enough people become fully aware of the results. Then it becomes almost unthinkable to do it again. Thank Hiroshima and Nagasaki for saving a lot of other people from burning up in the atomic fire. Maybe they saved you and me.