[tanknetter]

fearing something might happen is no reason to drop an atomic bomb on a city,

You speak as if the behavior patterns of the Japanese weren't known. In reply I'd give you Tarawa. Saipan. Guam. Iwo Jima. Okinawa. The list of examples where the Japanese demonstrated a very specific pattern of behavior in this regards goes on and on and on. It's almost easier to point out the exceptions (if there really are any).

There was no "fear" of something that was just assumed or hypothetical. There was solid, demonstrable knowledge, based on both past experiences and intelligence decrypts, that the Japanese were prepared to commit national suicide rather than surrender.

[The Red Zone]

And the Bomb was the most overall humane play possible in that situation. When the Japanese discovered that we were NOT out to massacre them back for massacring us, once they had surrendered, they said that Bomb had been sent from heaven. They were so right.