The best course of action was decided to be to bomb the population, FDR acquiesced to Churchill's desire, so they did. No apologies necessary, none desired.
The exact same arguments could be made about nuking Japan. Was it necessary? In both cases, the outcomes were the same, the wars were ended.
The nuking of Hiroshima and Nagasaki were necessary.
The war was NOT over for Japan at that point.
The US faced a ground invasion of Japan, as the Japanese military did not intend to surrender.
Even the bombing of Hiroshima did not convince the Japanese military to surrender.
And actually, neither did the bombing of Nagasaki.
There were elements of the Japanese military that tried to prevent the Emperor from broadcasting the surrender message to the Japanese people, even after Nagasaki.
About 150,000 people died in the two bombings. But it broke the will of the Emperor and the people to fight, regardless of the entrenched warrior code in the Japanese culture.
Those deaths prevented upwards of nine million Japanese dead and wounded, and one million Allied casualties, dead and wounded, by eliminating the invasion and conquest of Japan by ground and air.
Japan was isolated by August, 1945, but they were not out of the fight.
And for them, the war was not over.
It is easy for us to review the actions of 1945 from the safety and certainty of 2009, but, at the time, no one knew how it would end.
It ended in the most humane way possible.