Knowing a few couples with TCKs, I find it interesting that the lifestyle doesn't necessarily seem to come with liberalism, at least not a home-bred form of liberalism. Although they seem very comfortable with cultural pluralism, class seems to be an important part of identity, perhaps filling a void that might have been occupied by nationalism.
Yes, this is why TCK's are distinct from other groups. The idea of being in the cosmopolitan middle class replaces nationalism, which is one of the reasons they are so frequently hailed as perfect global citizens for a market-driven era.
Well I wrote in this article that Third Culture Kids are no different from refugees, immigrants, and other cross-cultural populations in that their "third culture" combines elements of the two into something new. Ideally, this would mean that they see even more value in social welfare, because they can identify with larger numbers of people. Unfortunately, it doesn't always turn out that way-- third culture kids can trap themselves into one cultural performance in order to ensure a lost sense of community, or identify solely with other TCK's which deprives their ability to empathize with larger groups of people. That is why it is so important to tackle the financial aspect of the identity-- it's also about privilege, which must be tackled if humanity is to be experienced to the fullest.