My dad was in the army and part of the invasion force. He told us (his nine kids) on numerous occasions that it is likely none of us would be here if not for the bomb (and the will to use it)
The fact is, the Japanese civilians were warned and ignored the warning.
And the fact is, far more people would have died — in total, and on both sides — had there been an invasion.
And the fact is, it is the right and duty of the President of the United States to put the lives of the US military ahead of those of enemy civilians.
And the fact is, had there been an invasion, the Soviet Union would probably have invaded in the north and the Japanese people would have suffered decades of a divided country, with half their numbers living under the crushing poverty and slavery of communism.