"Fat Man and Little Boy" not only illustrates the motives for creating weapons of mass destruction, but it also condemns the entire idea of the weapons. "Gojira" illustrates the mutually negative impacts of such weapons of mass destruction as the monster itself was disturbed by the weapons.
During the initial hypothesizing of creating the "device", scientists from "Fat Man and Little Boy" had positive motives for creating the weapon. The only reason for positiveness in such a dark subject was to prevent further life from being lost on the American side. Later information contradicts the previous thoughts of the creation of the weapon as the scientists are leaked information of the intentional use of the bomb. The motive of the US Government was to take a large amount of human life in an inhumane way to prevent further life from being lost on the US's side. During the resolution, many of the scientists disagreed with the creation and even the idea of such a weapon of mass destruction. Oppenheimer even publicly refused to support the creation of such a monstrous creation.
"Godzilla" was a creature that was disturbed by the weapons of mass destruction, which I find ironic that the monster was inspired by the idea of nuclear weapons, which in themselves are a monster. Godzilla was deemed indestructible by a scientist because of its ability to resist nuclear bombs that initially disturbed it. Another scientist, Serizawa, creates the "Oxygen Destroyer", a device that removes all oxygen surrounding it. The device is fairly inhumane but proves to be the only fighting chance the people of Japan, and possibly the world, have against this creature. Serizawa refuses to use his creation as it is morally wrong to him but as he sees the world around him crumbling, his thoughts are altered. In the resolution, Serizawa uses the device and engages "Godzilla", but he takes his own life during the process as he doesn't want the knowledge of such a monstrous creation circulating.
In both films, the scientists are faced with a test of justice behind the motives driving them to create these weapons of mass destruction. In both films, the motives are not just, but ironically they are carried out in the end and the weapons were created for better or for worse.