Discrimination on the basis of superficial factors exists. Positive discrimination on the basis of similar factors is inefficient for exactly the reasons you describe, but a) it's a lot cheaper and simpler than means-testing people to find out whether they're actually poor or just pretending to be and b) people often rely on superficial characteristics when choosing role models, which is natural because you want a model who's substantially ahead of you (otherwise you don't have much to aspire to) but the greater the gap you wish to close the lower the probability that you can establish personal contact with all the extra nuance and information involved.