Ralph Raico's Great Wars and Great Leadersseems to suggest that in World War II, the American public was even more vicious than the German. According to Raico, the American people clearly backed the nuking of Japan:
The political elite implicated in the atomic bombings feared a backlash that would aid and abet the rebirth of horrid prewar "isolationism." Apologias were rushed into print, lest public disgust at the sickening war crime result in erosion of enthusiasm for the globalist project. No need to worry. A sea-change had taken place in the attitudes of the American people. Then and ever after, all surveys have shown that the great majority supported Truman, believing that the bombs were required to end the war and save hundreds of thousands of American lives, or more likely, not really caring one way or the other.
The German people, in contrast, not only genuinely didn't know about the Holocaust...
[E]veryone connected with the killing of the Jews was bound by Führer Order no. 1, as well as by special orders from Himmler, mandating the strictest silence, under penalty of death. So it should not be surprising that, for example, the former Chancellor Helmut Schmidt, during the war a Luftwaffe officer, testified that he had never heard or known anything of the annihilation of the Jews; or that Countess Döhoff, publisher of the liberal paper, Die Zeit, should state that, despite her connections to many key people during the war, she knew nothing of the mass-killings in the camps, and that "I heard the name 'Auschwitz' for the first time after the war."
...but would have opposed it had they known. Raico approvingly quotes historian Sarah Gordon's conclusion that most Germans opposed the far milder atrocities of Kristallnacht. And he lauds Konrad Adenauer's hypersensitivity to the suggestion that the Germans ever abandoned the norms of the civilized world:
Some thirty years ago, when Israeli Prime Minister Levi Eshkol, at a dinner in Jerusalem, expressed to Konrad Adenauer his confidence that "under your leadership the German people will return to the community of civilized peoples," the old Chancellor retorted: "Mr. Prime Minister, what you think is of no concern to me... I represent the German people. You have insulted them, and so tomorrow morning I shall depart." It is impossible to imagine any recent German leader, in particular, the lickspittle former Federal President Richard von Weizsäker, responding with such unabashed patriotism, especially to an Israeli.
I'm afraid that Raico fails to make his case. Official secrecy is only weak evidence that the public would disapprove if it knew. Raico makes this very point about the U.S. government's efforts to conceal the horrors of Hiroshima and Nagasaki. The bombings were popular despite the official cover-up:
[T]he U.S. occupation authorities censored reports from the shattered cities and did not permit films and photographs of the thousands of corpses and the frightfully mutilated survivors to reach the public. Otherwise, Americans--and the rest of the world--might have drawn disturbing comparisons to scenes then coming to light from the Nazi concentration camps.
Furthermore, the fact that the Nazis gained power by largely democratic means makes it hard to believe that bitter anti-Semitism wasn't widespread in the German public. During wartime, this kind of hatred readily grows into acceptance, approval, or affirmative desire for genocide. Finally, as Timur Kuran's work reminds us, we should heavily discount people's stated opposition to the policies of a defunct, defeated regime. We expect random Germans after World War II to say "I didn't know about the Holocaust" and "I would have opposed it" - no matter what their true knowledge and feelings were.
The right lesson to draw, I'm afraid, is that the atrocities of both the American and German publics enjoyed at least the tacit approval of their respective publics. The man in the street might be vague about the details, but at the end of the day he rarely faults his government for injustice toward the Other.