I think that part of the problem might be that we tend to think of things like Jim Crow in quite impersonal terms, as an issue of education, employment, housing, and so on, in part simply because those were the sorts of issues that civil rights activists sought to address through legislation. Even lynchings tend to appear as statistics, as a number-per-year. That means we're left with a certain distance between the practice and the experience of Jim Crow, which makes cases like that of George Stinney appear incomprehensible. I think we need to be more prepared to draw out the psychology of white supremacy, try to join the dots between people thinking it was acceptable to exclude black people from a Woolworth's counter and thinking it was acceptable to murder black children. That's an alien mindset, a frankly terrifying mindset, and reading about relatively dry material such as housing segregation won't prepare you for it.
There have been admirable efforts to draw out the psychology of black people under Jim Crow, from the period itself onwards, but that's only one side of the story. Racist whites have remained something of an enigma, often a flattened caricature driven by sheer hatred, and that sort of stereotype doesn't hold up when you look at a case like that of George Stinney, where the racists have names and identities and appear to be otherwise normal, non-psychopathic people. You find yourself faced with something undeniably monstrous and undeniably human, and that's gonna mess with your head.