Take Journey to the Centre of the TARDIS as an example. Yay, we have 3 black brothers running their own business. But can the actors act? Hell no, they were awful. They weren't awful because they were black, they were awful because they were bad actors.
I guess one of the hard things about stuff like this is people see different things. You see three black brothers running a business but I couldn't help watching it thinking it was unfortunately suggestive that they were running a chop shop.