I know a couple of people who dislike umbrella terms - the best explanation I once had given by an asian friend was that she felt it was just inappropriate - she was asian, but she had no real cultural ties to India, she's been given a fairly normal middle class English upbringing, and as a result tended to find it ridiculous that she was presumed, by these terms, to have more in common with a first generation immigrant from Zimbabwe than with a white middle class English person, when she feels different.