Every August, you start seeing essays from professional and amateur journalists on the usage of the atomic bombs to end WWII. This month marks the 75th anniversary of that occasion, so you know there are going to be plenty more. And if this year is like all others, some of those essays will contain (or will have comments that contain) much wailing and gnashing of teeth about how we didn’t have to drop the bombs.
At least some of their reasoning involves post facto arguments, in that they use information that wasn’t available at the time. Or they rehash old, tired arguments that have been acknowledged and dismissed with justification.
What if we went back to the summer of 1945, and looked at the matter using only that information which was available at the time?