Because diversity is our greatest weakness, and this is true for both communities. The Jim Crow laws themselves were terrible, yes, but there is a reason many black leaders like Malcolm X were working to establish a black separatist state.
You should read some Thomas Sowell. During Jim Crow, black communities experienced the greatest increases in literacy, productive capacity, and economic standing in world history. On the other hand a mere 30 years of the welfare state was enough to destroy black families, black aspirations, and black progress, leading to the current state of dependency and squalor.