“Coming Apart,” which shot to No. 5 at Amazon.com immediately upon publication last week, has certainly prompted much conversation, if little in the way of consensus. David Brooks, a columnist for The New York Times, pre-emptively declared it the most important book of the year, saying, “I’ll be shocked if there’s another book that so compellingly describes the most important trends in American society.”

But to critics on the left Mr. Murray’s arguments are just an effort to change the subject. Defining the problem as one of cultural inequality instead of economic inequality, as the New York Magazine blogger Jonathan Chait put it, allows one to start talking about marriage and industriousness and “steer the debate back onto comfortable conservative terrain.”

Looking at America Mr. Murray sees a country increasingly polarized into two culturally and geographically isolated demographics. In Belmont, the fictional name Mr. Murray gives to the part of America where the top 20 percent live, divorce is low, the work ethic is strong, religious observance is high, and out-of-wedlock births are all but unheard of. Meanwhile in Fishtown, where the bottom 30 percent live, what Mr. Murray calls America’s four “founding virtues” — marriage, industriousness, community and faith — have all but collapsed.

The book says little about the roots of Fishtown’s problems, but in conversation Mr. Murray doesn’t hesitate to name the villain. “The ’60s were a disaster in terms of social policy,” he said. “The elites put in place a whole set of reforms which I think fundamentally changed the signals and the incentives facing low-income people and encouraged a variety of trends that soon became self-reinforcing.”

It’s an argument familiar from Mr. Murray’s 1984 book, “Losing Ground,” which established him overnight as a major policy intellectual and helped lay the groundwork for the 1996 law overhauling welfare. But in “Coming Apart” Mr. Murray’s recommendations are both more vague and far more ambitious. The first step, he writes, is for the people of Belmont to drop their “nonjudgmentalism” and lecture Fishtown on the importance of marriage and nondependence: to “preach what they practice,” as Mr. Murray puts it.