I agree we all harbor racist and bigoted sentiments and that the vast majority of us overcome those sentiments. I'm just looking for reasons why Americans tolerate those who not only can't but are compelled to express their mindless hate.
The following is a small part of it (IMO)
Racism lubricates imperialism. (By imperialism I simply mean the way in which a superpower extends its influence over geopolitically vital (or resource rich) territories. There are many forms of imperialism, e.g., colonial, which involved direct military engagement, and post-colonial, which involves the forcible opening of markets to outside investment, e.g., consider what happened to Mossadegh when he refused to play ball with Western energy needs. He was replaced in a CIA coup by the brutal Shaw)
When the west expanded from Europe to the middle east and the global south for economic reasons . . . it claimed to be civilizing the savages. It cloaked its mission in messianic nationalism - the redeemer nation saving the world, ridding it of evil, i.e., [cough]getting salt[/cough]. Same thing with the settling of America. In order to seize territory . . . in order to co-opt resources like land or oil you have to claim that the people whom your are killing or controlling or "saving" are savages, i.e., culturally/morally inferior. Same thing with slavery. If your economy requires free labor, than you have an interest in seeing blacks as morally akin to animals. Indeed, consider woman. To justify their unpaid domestic labor and exclusion from the political process, men called them hysterical and irrational - and unfit for public life. This is part of why they could not vote.
When your economic needs mandate that you intervene in the fate of another nation, it's easier when you think that nation is inferior or evil. So the mind obliges your needs with a rationalization.
In terms of why some Americans tolerate Nazism. Consider the Nazi position on white anglo supremacy. Remember: nazism hated liberal tolerance. It believed that there were real Germans and false Germans - and that the false Germans needed to be expunged
not tolerated. It was ultra Conservative in that it wanted to protect German borders, language and culture from the over assimilation of the Jews, which accelerated during the very liberal Weimar period. Once you understand the connection between the
Institute for Historical Review and David Duke - you will see how compatibly white supremacy and nazism fit into the "real Americans" rhetoric of Palin and Limbaugh.