Ever since the Civil War, Southern White folks are aware of the horrible injustices done to Black people (who include rather a lot of slaves that were fathered by White owners) and fear that the former slaves would treat them as White slavers were treated in the many slave rebellions that took place in the Caribbean and Brazil. Newspapers were filled with these lurid tales.
After the Civil War, there were far more attacks of White people on Black people and this continued all through the Jim Crow Era. And now Mark wants to reinstitute Jim Crow because he apparently has nightmares of being attacked by George Floyd. he wants all Black offenders executed or thrown into prison, all Black politicians to be defeated at the polls and all Black people to continue having one dime of assets compared to the dollar owned by White folks.