Prejudice has been at the base of America from the day it was born. African Americans were bondaged for the majority of American history and segregated for most of the rest. These two concepts wove their way into the text using the black John Jackson. For instance, after his fortune is told, the judge and even Tobin (who dislikes the judge) keep the clearer meaning from him. The judge tells him that "All will be known at last. To you as to every man." I think this hints at the fact that he is somehow infereior now and will soon ascend to their status in the future.
There is also an extremely funny encounter between the owner of a restaurant and the Glanton Gang. The owner puts his hands down on the table and said, "Gentlemen...we don't mind serving people of color. Glad to do it. But we ast for em to set over here at this other table here. Right over here." Someone from the gang says, "He thinks were niggers." Glanton then says, "Mr Owens, if you was anything at all other than a goddamn fool you could take one look at these here men and know for a stone fact they aint a one of em goin to get up from where they're at to go set somewheres else." After a little more talking, Brown gave the owner a gun and told him to shoot the nigger. He didn't want to but in self defense. But Jackson killed him first. Basically, they were testing the owner with Jackson's life. Even though they knew he would win, it was still a cruel test with which to make him pass.
The idiot, before his demonic baptism by the judge, is basically a retard (hence the name idiot). The way society treats him is by putting him in a cage for all to see, as if he isn't human. Around this time period, Dorothea Dix led a crusade for the mentally ill. She argued in her report to Congress titled Memorial that there are, "Insane Persons confined within this Commonwealth, in cages, stalls, pens! Chained, naked, beaten with rods, and lashed into obediance." This paints a clear picture of how the idiot is treated. In America, prejudice towards the mentally ill has become more of a social isolation rather than a physical one. But that doesn't mean that society as a whole cannot care more for them. For instance, if it leaked that someone met a psychiatrist once a week, then that person might be labeled as psychologically unstable and be shunned be people for no truly solid reason.