No argument about horrific acts of the Japanese in WW2. The fact that all sides attacked soft civilian targets across almost the entire theatre of the war does not absolve anyone IMHO. Dozens of Japanese cities had been conventionally bombed before the Potsdam declaration, which the Japanese evidently failed to understand or to take seriously. The threat of an atomic bomb attack or demonstration of it against a military target (as intended at Nagasaki) would probably have stopped the war without requiring another quarter of a million or so mostly innocent civilian casualties.
If the Japanese had managed to drop one on Sydney I'd expect you may have a different view.