You know, taking it seriously now, I actually put forward a question in a debating thread about the nukes of Japan. I got this back.
'The bombing of Japan was the beginning of the Cold War. You can list all sorts of reasons for it, but its really simple. Germany had just been defeated a few months before, and Russia had begun the process of controlling East Germany. The Potsdam Accord was signed on Aug 1st, with France signing on Aug 4th. None of the western nations liked it, but they were trying to prevent another war between Russia and the US/UK. Patton had already suggested invading Russia since the troops were already there, and Churchill had drawn up some plans. It was as tense a situation as there can be, so the accord was signed. Russia then declared war on Japan, they had been neutral towards each other up until this point though Stalin had agreed to declare war after Germany was defeated. He did as he promised, but Germany was defeated in April when Hitler was killed and officially surrendered on May 7 and he waited until he forced the other allies into giving up half of Germany before he committed to war in Japan.
On Aug 6th the first bomb was dropped on Hiroshima. They had already been planning a full scale invasion of Japan, with Russian help already promised. However the US, UK, and France were nervous as hell about Russian involvement after what happened in Germany. My opinion is that the bombs were dropped so that Japan would surrender to the US, and not to Russia. Technically they surrendered to the allies, but they did so before Russia could move troops across Manchuria and secure any of the Japanese held territory for their own.
It wasn't about the number of soldiers that would be saved trying to island hop across the Marianas, it was about ending the war as fast as possible to limit the spread of Soviet communism.
What most people don't realize is that the targets of the atomic bombs, including those not actually bombed, were going to be firebombed if nukes weren't used. Nuking a city takes one bomb and one mission. Firebombing, and this was the case with the infamous Tokyo firebombing of "Operation Meetinghouse" (March 9-10, 1945), including multiple raids on the same target. Tokyo was hit more than once. So, Hiroshima and Nagasaki and all the other cities spared conventional bombing because they were potential nuke targets would, I would argue, have suffered more casualties if they were conventionally bombed. Another tidbit most don't realize is that we kept bombing Japan even after Hiroshima and Nagasaki were nuked. Japan was going to be burned to the ground whether or not "Fat Man" and "Little Boy" were dropped or not'