> but you have nearly entirely white cities like Portland that also experienced their own explosive suburban growth in the same time period

Yes, it was exactly my point that Portland was already the whitest metropolitan area in the country. And yes, I am well aware of the extensive redlining (my grandparents lived in Vanport before it was destroyed). And yet they still had people explode out into the suburbs through the 50s and 60s.

This is a counter-example to the thesis that urban flight was purely a racist response to "preserve apartheid".

No one is arguing that racism didn't exist. But suburbanization happened everywhere around the world where cars were introduced (even places with almost no diversity). To blame suburbanization as a purely racial phenomenon is not true.