I totally agree with the reasoning at the time to go ahead with the Manhattan Project. We didn't know if the Germans or Japanese were close to creating an atomic bomb themselves. But after the war we learned that neither the Germans nor Japanese were anywhere near close. On the other hand, thanks to Klaus Fuchs and other pro-Soviet workers on the Manhattan Project, secrets were passed to the Soviets (yes, our allies in the war, but everybody knew that after the war that they wouldn't be) that allowed the Soviets to build their own bomb just 4 years later. In retrospect, without the Manhattan Project, who knows when anyone would have invented the atomic bomb. Maybe nobody for decades.