I can't imagine sitting in a theater in 1954 in Japan and watching "Gojira" play for the first time. Ten years earlier, your country faces a nuclear nightmare, and for the first time in human history, the atom was used to wipe a city full of people off the planet in an instant. War reached its most horrifying manifestation, and it completely changed the world. But for Japan, it was not an abstract. It was a redefining moment, part of their identity from that moment, an actual scar they were going to have to live with. Looking at "Gojira" now, it feels like an attempt to come to terms with the hopelessness of that event in a way that people could watch together, a fantasy catharsis that the country needed.
The stark black-and-white images of a giant monster smashing and burning Tokyo must have felt terrifying. Godzilla is barely a character in that first film. He's a rampaging force of nature, and the solution they find to finally stop him is pretty much an equal horror, a worst-case-scenario sort of ending. They know that if they use it, they're turning Tokyo Bay into an aquatic graveyard. To kill Godzilla, they're going to have to kill everything, and that seems like an acceptable trade.