I’ve been asking this question for years and have yet to be answered:
Name just one single place where black people have moved into in significant numbers where it was cleaner than before, crime rates went down, and it became more prosperous.
Here’s an exercise to try (which illustrates your point). Look at the black % of the city’s population and guess the murder rate. Or look at the murder rate and guess the black % of the city’s population. Try it for any city =>