I've had racist abuse yelled at me in the street - and not just the street. We all have.
In the past, I've tended to do what Wells is saying: walk away. Not because I necessarily thought it was the right thing to do, but because I was afraid that the situation might escalate into violence.
It left me feeling diminished, for two reasons. One, because I'd been racially abused by a stranger, for no reason. Second, because it left me ashamed that I didn't have more courage. I was more concerned about the possibility of some pain, than I was about doing what is right, and standing up for myself.