I don't think there is anything wrong with considering the diversity of a place when considering where to apply. If you ask people why they like London or another big city, diversity usually comes pretty high on the list. Saying that you would never go somewhere because there weren't people of the same ethnicity would be retarded in my opinion, but to each their own.
As someone who is in a minority in medical school i can say it wasn't the be all and end all, but it was a consideration. I wanted to do medicine enough that i would have gone anywhere, but i would also pick somewhere more diverse over somewhere that is less intergrated.
I know of someone in medical school in newcastle who is black and it is more of an issure for her than it is for me.