Except diverse communities in Finland do not have significant achievement gaps with non-diverse communities.

Edit: After looking into it PISA stats, this is inaccurate. Must have heard this in a news story.

Edit 2: They do seem to do better than us with diversity - http://www.compareyourcountry.org/pisa/country/fin - but worse than OECD average.

That seems like an odd tangent rather than a rebuttal, but it would still be interesting to see such data.

I think that brings up the question, does the homogeneity of a country really mean less concern for "paying for other people's kids", and how do we define homogeneity: culture? income level? family size? ethnic background? net wealth?

What do you mean by homogeneous?

It means people view each other as being part of the same tribe, or network. People (and many other animals) don't mind helping people in their "closer" networks, but the further away you get in the network, the less you care about someone else. Perhaps it is because there is an assumption that there is less reciprocation the further out you go in the network.