Several Nazi generals, in fact, thought Hitler was insane for having declared war on the US because they knew, and most Brits knew, that the US couldn't get a declaration of war against Germany passed through Congress unless and until some act far worse than the sinking of freighters or destroyers.
Twice US ships engaged in such duty were attacked the Congress still refused to even consider a declaration of war against German because the vast majority of the population didn't want Roosevelt being involved in another European war even if it was just escorting and protecting US freighters carrying US goods to England.
Once the war started, all bets were off. People knew how the Japanese were slaughtering and torturing civilians in China and they knew the Germans were letting hundreds of thousands of Russian POWs and civilians starve to death as well as killing many civilians just to avoid dealing with them in occupied areas, and not only Jews. Hitler spoke on the radio about all Slavs being subhuman. People in the US could pick up those broadcasts and they were printed and published in many newspapers so no one was in the dark about what sort of animals we were up against.
Maybe not the rank and file, but the rank and file would follow orders and at the leadership in both Germany and Japan considered others as subhuman animals unworthy of living on the planet with them except as slaves.
Using A-bombs on Japan was merciful, not horrible, and millions of Japanese survived the war because we used those bombs rather than invading, not to mention the million or so dead and wounded US military folks who were spared.
Any other opinion of the issue is based on an unrealistic revision of history to suit the agenda of the person(s) spinning the alternative viewpoint.
If it was just Jews, then that’s a different matter?
Once Britain also declared war on Japan, that basically ended any limits on aiding Britain. Inevitably we would up our supplies to Britain and the Germans would sink US ships, giving us the Casus Belli to go to war with Germany, it was only a matter of time.