I understand that before abolition there were many arguments for enslaving Africans (inferior intelligence, they needed to be cared for, etc.).
What was the basis for white hatred and violence toward the black community long after emancipation? Events such as the June 21, 1921 torching of "Black Wall Street" north of Tulsa seem absolutely ludicrous to me. Can anyone share insight about the racist mindset?
You need to look at the importance of demographics, especially in a democracy. In many Southern states blacks made up (and still do) a large proportion of the population, and in a democracy, this translates in theory to political power, meaning the possibility of a feeling of threat and fear for the white population.
In Oklahoma in 1921 I'm not sure if this demographic factor was really present though. If the stats were anything like today blacks form only a small part of the population. However the incident that started it all (black Dick Rowland accused of attacking white Sarah Page), is literally the classic scenario for starting off an ethnic riot, there are innumerable examples all over the world throughout history. So in this case the basis for the animosity could have been anything - but when it comes down to it it's plain old bog standard ethnic hatred.