Martha Jones Deserves So Much Better.
In general, the Russell T. Davies era felt pretty diverse for its time, but the way it treated its black characters feel .... wrong. Like, listing out all of the notable black characters in the 9th and 10th doctor era.
Mickey Smith - Spends 90% of his screentime on the show being made fun of and being treated as a joke. Gets unceremoniously abandoned by Rose for the Doctor.
Martha Jones - Travels with the Doctor for a season, spends two months in racist-ass 1913 Britan stuck taking care of him and working as a maid, and then spent an entire year watching the entire planet being tortured and seeing massive genocides by a crazy dictator, while her entire family is forced to work at maids. Also she somehow ends up with Mickey???
Honorable mention to the two characters from the End of Time. I have no idea what the hell was going on there, but it made me hella uncomfortable.