Cultural kin selection can act to magnify kin selection psychology - as we see with sports teams for example, which use relatedness and unrelatedness superstimuli.
It is not that hard to imagine that we get to a point where iPhone users won't date Android users. Political polarization illustrates a similar divide. Too many memetic differences make people treat others as though they are not part of the same species. They unconsciously don't want to interbreed - as though through fear of infertile offspring. This is not to say that they literally fear this, it is implemented more as a kind of revulsion.
Hamiltonian spite is generally thought to be a fairly minor effect - harming others offering more costs than benefits. However, cultural kin selection puts another spin on the issue with its superstimuli and psychological manipulation.
Cultural kin selection - essentially the science of shared memes - seems like a critical tool for studying these issues to me. I've previously called for a science of racism. Perhaps a better plan would be a science of xenophobia. Much xenophobia is cultural origin - due to lack of shared memes - rather than lack of shared genes.
One interesting suggestion relating to political polarization is that it arises - in part - as a battle between hedonism and survivalism - with the "right" being survivalists and the "left" being hedonists. Framed in terms of heritable information, that would be the right favoring DNA and the left being more on the side of memes and psychological replicators. That's not my idea - and I don't know what to make of it. I generally view most "left" and "right" parties as "absurd churches", and avoid getting involved. So: I'm not much of an insider and don't know what many of the doctrines are. I do think the idea may have some truth to it, though.
Update: The idea that the "right" are survivalists and the "left" are hedonists came to me from Curt Welch. The nearest thing I can find to a public discussion of the issue by him is here.