What if Longstreet had managed to launch a morning attack on the second day instead of late in the afternoon on the Federal left wing at Gettysburg?
What if Hitler had not delayed Barbarossa to assist in the Balkans?
What if the Japanese had launched a second attack at Pearl Harbor and destroyed the fuel supplies?
What if, what if, what if. Despite the misgivings of Eisenhower and others Truman obviously had advice from many that it was necessary to use the bomb to force Japan into a quick surrender. As for killing innocents, the fire bombings in Japan and Germany had been doing that already for some time.
Armchair Generals armed with 20/20 hindsight are a dime a dozen.
Longstreet only had one division on the field that morning (McLaws was not yet up and Pickett was miles away) and Sickles' Corps would not have moved into the salient yet thus Longstreet's defeat would probably have been much worse.