changing the races of people - except the author didn't change the race of anybody. She selected a historical person of interest and sent him somewhere plausible. Marshals chase fugitives, after all.

What is clearly desired is for her to not select a black Marshal.

tendency to do something equivalent to saying that it's a "problem?" - in this case, the tendency to whitewash history means that we, as a society, forget that not just whites participated in history. In short, whitewashing is the problem, and the only way to not whitewash is to actually put, where historically plausible, non-whites into history.