The US is the only country to have used nuclear bombs in anger, and that was during it's nuclear monopoly.
Using a new weapon to end an existing war is one thing. Using a new weapon to start new wars is another. That delineation is independent of one's judgement of the weapon per se. They're both bad. But one is worse than the other.
The U.S. had the opportunity to go on a mission of global military conquest. There was military support for nuclear war with Russia and China. The United States didn't do that, and I think that's a unique and admirable trait.
Yes, using nukes defensively is less bad than using it to start a war. That doesn’t mean I support the use of nukes.
WWII was unique in starting with no nukes and ending with them. We also didn't yet understand the long-term ramifications of the weapon's use.
After the failure of the Treaty of Versailles at the end of of WW1, resulting in WW2, the Allies learned that unconditional surrender was needed to prevent future wars.
The Japanese military command preferred that their troops never surrender.
So the 2 options the US had were:
1) Curtis LeMay would use 10,000 bombers to napalm those cities, and every last village in Japan.
2) Use 2 nuclear weapons and demand a surrender. The military commanders in Washington debated the ethics of using such weapons, so this wasn't done lightly.
Having studied this over a period of years, #2 makes the most sense to me.
And Japan and the Soviet Union had been at each others throats since before there was a Soviet Union and Japan thumped the tsar.
I am sure Japan did not want to surrender under a Soviet flag that was looking for 50 years of retribution.
In a strange way it was an American coup to get peace signed before Russia started stripping the place down to the bone.