Well, it's like the restaurant example.

If I search for "restaurants", it shouldn't give me restaurants in Shanghai because that's the city with the largest population. It should give me Northern California, since that's where I live and Google knows that.

Similarly, Google might reasonably infer that if someone is searching for their own race, sexuality, or religion, they're probably more interested in information or support groups than porn. Not that both can't be served as results... just... priorities of what people are looking for.