Well, for me it was more a kind of "let'S try out how fine this bomb works"-thing for the scientist, but of course he was influenced by them.
I have no idea how long it takes to clarify a situation and I, of course, don't know, whether he waited before etc., but I just believe, that it could have been avoided, if there had been a more careful research before, because of course, you can't just launch such a bomb, without a research before, .. or can you? I don't know, how it has been handled in this particular case, just that we know today, it wasn't necessary, so the chances he could've known it wasn't necessary are not impossible, so I see the possibility of another solution back then, so I don't think it can be justified that easy. (ok, that sounded somewhat chaotic, but I hope a bit understandable 😖)
Perhaps it was the best solution..we don't know. But I believe, there could have been a more peaceful way to ensure .. peace.
And the attitude of the current president of the United States doesn't show too much .. "learned".
((I didn't get the part with "Japan was -satisfied-"😉)