You need to think a little more deeply - why should blacks moving in cause home values to plummet?
Property value is directly related to supply vs demand. When whites discover that most blacks do not prioritize keeping their property in good shape, they start to move out. Then others quickly follow.
Mumbles thinks it is racism but I honestly think it is concern over property value. Because if it was racism alone, the whites would simply rent out their properties to other blacks and not sell out at a loss. Instead, they fear holding on to property that is quickly deflating in value. If blacks moving in caused property value to increase you would never see whites selling even if they could not stand to live next to blacks. They would hold on to an asset that was rising in value (like property in California for example).
It is like a bank run. And as more and more whites flee, property value drops to the floor. As an owner of multiple rental properties, Ive seen this often enough that I am concerned not to lose money myself.