I seriously doubt cars cause a "racial divide" in any reasonable way.
As for whether I think it's a "reasonable tradeoff". I don't know, but maybe because it's not brought up as controversial by society. This is not a good reason, I suppose, but I haven't really thought about it. I guess I'm mindlessly mimicing the ethics of people around me.
Unrelated but curious, why do you feel it's a completely reasonable tradeoff? In my mind, automobiles have led to a class (and historically race) divide which further segregates and polarizes sects of society.