They dropped two nuclear bombs on Japan to make the Soviet Union's invasion of Hokkaido unnecessary and as a performative act to horrify the world in to subjugation.
The whole 'saved more lives than it cost' is a bad argument unless the plan was to slaughter a hundred thousand civilians on landing. Note the Nazi invasion of France cost 60,000 lives in civilian resistance...this was at the beginning of the war.
Japan would have surrendered on the first day of invasion.
You cannot convince atom bomb supporters of this. They fully believe that Japan would have held out until every man in their army was killed just to spite the US.
shitwehraboossay spent a frightening amount of energy trying to justify the nukings along those lines iirc
Not saying that's correct but it did take 6 days after the nukes for them to surrender.