> If what you are describing were anything like reality, the battle for Civil Rights would have been over a hundred years ago and we wouldn't be having this discussion, at least with respect to discrimination in mortgage loans and other financial instruments.
Jim Crow laws were enforced until 1965. They existed in the lifetimes of part of the current generation of would-be homeowners, and that is one thing you can't lay at the feet of the banks.
> All it takes is a cursory glance at almost any mass migration in the US to show why that amplifying effect doesn't exist: when the [x]% finally get the money to move in, everyone else usually moves because of prejudice, driving the value of the neighborhood down and the [x]% into bankruptcy or financial destitution. I can even name a few towns in California where this has happened in my lifetime.
The events you're describing should have the opposite effect. The first family to move in is obviously screwed, but screwed in a long-term sense where they lose the value they paid for their home which only happens in some decades when they want to sell it. Until then their mortgage payment is the same one they budgeted for to begin with. And all the racist white people who are leaving are in the same boat, but right away -- they want to leave but no one will buy their house for what it was worth last year.
Meanwhile there is suddenly a whole neighborhood where housing prices have plummeted and a bunch of white people who would otherwise come in and bid the prices back up are opting out. Doesn't that just make it easier for other black people to buy those homes for a discounted price?