The problem with that is, Japan was willing to fight on after the first bomb. They tried labelling it a natural disaster at first; if the second bomb wasn't dropped, they probably wouldn't have surrendered. Sure they could have waited longer to confirm that, but then there's more troops dying on both sides while they wait - more unnecessary deaths.
Okay, so the Japanese lost lives in every major battle, with the deadliest battle being the Battle of Okinawa in 1945. During the two-month battle over the island, over 100,000 Japanese soldiers died and 12,000 American soldiers died.
For comparison, in the three days between the bombs anywhere from 129,000 to 226,000 civilians were killed.
There is no comparison and no justification.
