Culture at the Dawn of the Atomic Age (1994).
Boyer pointed out that a small-but-tenacious minority held firm in their moral beliefs about the atomic bomb in the first few years after Hiroshima. Although never truly united, churches were the "greatest voice" against the use (and future use) of the atomic bomb. Their argument was based on the belief that the moral cost of using the bomb was too great, and that the Japanese were the equal of Americans in terms of the sanctity of life.
The popularity of John Hersey's Hiroshima in 1946 seems to indicate that quite a few Americans were at least leaning towards that viewpoint. In its extreme, the religious moral view was eschatological in nature; in other words, America will pay for its use of the atomic bomb on "Judgment Day." Another moral viewpoint against the atomic bomb came from the African-American communities, in that they were openly questioning why the atomic bomb was used on non-whites, instead of, for example, Germany or Italy.
Most Americans regarded the atomic bomb in terms of security after Hiroshima.
Increased worry about destruction was a greater concern than not only moral objections, but also to peacetime applications from the atomic bomb. In part, that was due to the effectiveness of the U.S. government and military controlling atomic-related information, shaping the public's perception of "all things atomic." I think the government was largely successful in encouraging the public to see the atomic bomb in terms of security instead of morality, in that most Americans were inclined to place less emphasis on the past and present, and focus on the future. The view towards security allowed the luxury of looking towards the future, instead of analyzing (and agonizing) over the past and present. The "Science Movement" fits this model, in that while individual scientists lamented the use of the bomb, the movement focused on increasing the security of nations with a new international order in the "Atomic Era."
By the late-1940's, "Atomic Morality" became equated with pacifism; in other words, the "Atomic Debate" became centered around "Morality AND Security." By this time, the atomic bomb, in the eyes of more-and-more Americans, was justified and "morally praiseworthy." Boyer mentioned that the increasingly common view, by around 1949, was that "God meant for America to have and use the atomic bomb." In particular, after the U.S.S.R.'s first successful test of its atomic bomb in 1949, WHO drops the bomb started to matter - and America is the only "Good Guy" with atomic weapons. As Boyer asserted, once that threshold was crossed, there was no going back.
By the late-1940's, most Americans had an increased desire for the U.S. government to have an "Atomic Supremacy" over the U.S.S.R.; which basically meant build bigger-and-better bombs compared to Russia. When the first test of the hydrogen bomb was announced, the level of moral objections in America were nowhere near those after Hiroshima. The fear of the Soviet Union was greater than any "Atomic Morality", and the increased focus on civil defense trumped moral consciousness as well by 1950.
Within five years after Hiroshima, the debate centering around the use of the atomic bomb had shifted to a national security strategy based on the belief that the U.S. was morally entitled to have an "Atomic Supremacy" over the U.S.S.R. This nuclear deterrence strategy created, as Boyer called it, an "Illusion of Diminished Risk" that formed a basis for how Americans coped with the possibility of nuclear war.