For the same reason, we should be wary of discriminating against individuals in the present, because their (putatively) racial forebears had advantages in the past. It’s tempting to do, because the results of this previous injustice may still be apparent in statistics today – the number of black women novelists, or Oxbridge graduates, say, may still be very low.
But if the injustice no longer afflicts you, personally, and no longer benefits the individual you are confronting, (perhaps you have an Oxford degree and/or a publishing contract[1]; perhaps they achieved theirs on personal merit), then, surely, you are using assumptions about their perceived race to dismiss them. You are attempting to gain, or maintain, an advantage for yourself and your own clan, even if it is just the privilege of moral superiority.
This is the motivation of all discrimination by all privileged elites: to try to keep the good stuff for themselves. By reproducing such behaviours, you justify all previous discrimination, because the grounds for objection to their historical monopolies is that they were unfair to people as individuals. You are removing the moral principle from your argument, so that all you are left with is grievance and anger and protests that demonstrate not consensus, but raw power.
A social activist, quoted in the Guardian, recently, claimed that the protests of the last year had made a lot of progress, because they generated fear.
That conjures up frightening prospects.
[1] the two often correlate
Middle-aged Male Anorexic 