Right.... Myth repeated many times becomes truth.
This myth is plainly obsolete and no longer withstands criticism now that WW2 facts are freely available.
If we were really that concern about saving human lives, we should have exploded Little boy and Fat Man in the same desert, in the presence of enemy nation's, Japanese, military representative and allowed them to film.
Hell in 1945, several month ago, Tokyo has been fire bombed and there were more victims in Tokyo (a total more 200,000 people - 90,000 dead and 125,000 injured), than Hiroshima and Nagasaki combined. More casualties did not bring quick end, but less casualties brought quick end.... this is the perverted logic that is being repeated again and again.
This self-righteous JUSTIFICATION is plainly ridiculous. There is no and cannot be Justification or Rationalization.
The fact is that this WAS a new weapon, and US had a vague idea of the power and consequence of the weapon and the war was a GOOD justification to test the weapon on Japs.
The fact is that at that stage of the war both sides have been committing war crimes.
In a fictional scenario where, for example, Germany dropped a nuke during WW2 on London, they would have been tried for the crimes against humanity.
The fact is that the Victors are not tried. Not for Dresden (designated children refuge) bombing, not for passenger ship Wilhelm Gustloff (10,000 civilian sank), not for many other war crimes that were committed in the name of "victory"