Current worldwide densities:
I can't see how you can attribute US social pathologies primarily to population density, since they're not particularly extreme.
These factors and the anxiety they produce feed into consumerism, materialism, spiritual impoverishment, deviant sexual behaviors, increased female aggression/male passivity, more hostile winner-takes-all competition, etc., which takes us to the society we have now. Note that many of these symptoms exacerbate this anxiety as well.
Societies that have retained a strong uniform cultural identity and traditional behavior will of course have more leeway when it comes to population density.
I think the conceptual space is imploding rapidly before our very eyes. The liberal shift to "homeschooling IS NOT JUST FOR FUNDIES" is evidence that they're bailing the ship they've sabotaged (count the number of references to diversity, btw):
One of Dimitry Orlov's readers sent this in and I think it's true. We're moving to a post-USSR style implosion of conceptual space:
Even Red China has more conceptual space than us: