I thought the fact that Martha was a servant while the Doctor was a teacher said more than the racist joke.We had this same debate fifteen years ago when Freema Agyeman was cast, and we got some evidence of how the show would deal with it: by ignoring (“The Shakespeare Code,” where the Doctor tells Martha to just act like she owns the place) or incorporating (“Human Nature,” where one of the students makes a racist joke at Martha’s expense while she’s posing as a servant) it depending on the tone of the story.