The issue is that the military officially stated a reason. The other reasons are hearsay or undocumented rumors, but look at our actions surrounding Russia/USSR activity. We never liked them, were determined to "stop communism", etc. If we hadn't decisively cut the war short, the Russia would have gone into Indo-China first, and that would give them a majority of Asia. Fun Fact: The Emperor of Japan was against the war from day 1.