Mark's blog on the Charles Murray book, Coming Apart, gets to the heart of the question:
At the risk of stating the obvious, I think the most fascinating part of this discussion is how income inequality and cultural inequality interact. In particular, I wonder how much of the decline in "virtuous" behavior that Murray observes among the poor is a result of choices driven by poverty (scarcity), and how much have those behaviors perpetuated that poverty….And by the same token, the wealthy can certainly be applauded for their virtuous behavior, but to a certain extent it is easier to be good when you have the means, and the extent to which this plays a role should be acknowledged as well.
These questions are explored at some length by David Frum, "Is the White Working Class Coming Apart?" (Note: this is a link only to Part I.)
As it turns out, Mark's intuition was pretty good in honing in on the main problem with Murray's thesis: Murray observed correlations but may not have the tools to discern causation. Rather than a values decline leading to economic decline, as Murray claims, why not consider the reverse?
With pay and prospects declining for high school graduates after 1960, fewer men entered into (or stayed in) long term marital relationships. Economic misfortune leads to values collapse. This reversed the trend of the first half of the 20th century, a period in which progressive policies (minimum wage, child labor laws, Social Security) greatly improved the lives of high school graduates—at the cost of greater government intrusion.
Frum therefore reached this startling conclusion:
As I looked backward and forward in time, however, I had to face this awkward fact: America became more culturally stable between 1910 and 1960 as it became less economically and socially libertarian. As it became more economically and socially libertarian after 1970, America became culturally less stable.