The Second World War, as a whole, was probably the most catastrophic event in humanity's recorded history. The world was pretty much screwed as soon as it started -- indeed, probably as soon as Hitler acquired control of Germany.

For the purpose of saving humanity in the future, it may not be most effective to focus our attention on particular decisions (even apparently large ones) made during the course of the war (indeed, near the end of it); we risk missing the forest for the trees.