Why do we pretend that it's some sort of virtue to be unconcerned with those we surround ourselves with? It's no virtue. After all, why are we here on HN instead of Digg or Reddit? I'm sure a demographic analysis of that switchover would yield similar results.
Well, because class stratification denies opportunities to people who are born to the wrong parents, drastically reducing the pool of innate talent that can actually be applied to solving society's problems, maybe. Or because lack of interchange between social groups brings those groups to misunderstand and fear one another, leading to violence between them (Japanese internment camps being an example inside the US in…
Though I suppose as a researcher you could have some fun by creating fake accounts with different profile pictures and start adding friends randomly.