Do you think the author seems optimistic or pessimistic about race relations in the United States?
Well, actually, neither. He seems realistic. He seems to say that there will be surges of fear unlooked for, in people who consider themselves free of racism, and that race relations with always surprise us.
But if I had to say one or the other (rather than realism), I'd say pessimistic. He seems to say that unconscious pockets of racism will outlast conscious tolerance.