Well, here's
Humanity's take on that:
The restraining effects of moral identity can be weakened by evading any clear recognition of what you are doing.
In his private diary Truman wrote a passage on the bomb. Given the decision he was making, there is something disappointing about the quality of his thought: [diary quote]
The passage gives evidence of the need to escape from any clear, plain statement of what he was about to do. There is the denial of the full human impact of the bomb by seeing the victims as ‘Japs’ and savages. There is the half-suggestion that the bomb may not work anyway: we only ‘think’ we have found a way to split the atom. We are exonerated because we are giving them a warning, even though we know they will ignore it.
Above all, there is the evasion of the fact that an atomic bomb dropped on a city cannot possibly be directed at purely military targets. In Hiroshima civilians outnumbered soldiers by more than six to one. President Truman certainly had some idea of the civilian casualties later. After Nagasaki he stopped the atomic bombing, saying that the thought of wiping out another 100,000 people was too horrible, and that he did not like the idea of killing ‘all those kids’. Perhaps at some level he knew about this before Hiroshima. If not, his concern for the children was too small to prompt him to find out.
It was not only the President who had to face or evade a moral decision. The scientists who developed the bomb were also faced with a question of conscience. While some confronted it, others took refuge in evasion.