In one sense, this method is like the method of geometry that Euclid had given to the world in that one began with self-evident truths as axioms and then deduced by equally self-evident steps a set of theorems. Descartes referred to this as the “synthetic method” of doing geometry and (he had hoped) physics.
It would be because the atomic bomb was a new superweapon, and napalm had been around for a while. Does that make it right? No, but what had to be done had to be done.