I don't know why so many people have a problem understanding this. It's pretty simple. We're dealing with 2 different volatile compounds. One is called SPB (stupid poor black people) and the other is called SPW (stupid poor white people).
SPB is found mostly in inner cities where it tends to be more concentrated which increases the frequency of interaction so the potential for a violent reaction is much greater. SPW tends to be more diluted across the country in the more rural areas where it finds far less opportunity to react with either SPB or more SPW.