So, this is a puzzle. If you look within the United States, religion seems to make you a better person. Yet atheist societies do very well—better, in many ways, than devout ones.
The first step to solving this conundrum is to unpack the different components of religion. In my own work, I have argued that all humans, even young children, tacitly hold some supernatural beliefs, most notably the dualistic view that bodies and minds are distinct. (Most Americans who describe themselves as atheists, for instance, nonetheless believe that their souls will survive the death of their bodies.) Other aspects of religion vary across cultures and across individuals within cultures. There are factual beliefs, such as the idea that there exists a single god that performs miracles, and moral beliefs, like the conviction that abortion is murder. There are religious practices, such as the sacrament or the lighting of Sabbath candles. And there is the community that a religion brings with it—the people who are part of your church, synagogue, or mosque.
The positive effect of religion in the real world, to my mind, is tied to this last, community component—rather than a belief in constant surveillance by a higher power. Humans are social beings, and we are happier, and better, when connected to others. This is the moral of sociologist Robert Putnam's work on American life. In Bowling Alone, he argues that voluntary association with other people is integral to a fulfilled and productive existence—it makes us "smarter, healthier, safer, richer, and better able to govern a just and stable democracy."
The Danes and the Swedes, despite being godless, have strong communities. In fact, Zuckerman points out that most Danes and Swedes identify themselves as Christian. They get married in church, have their babies baptized, give some of their income to the church, and feel attached to their religious community—they just don't believe in God. Zuckerman suggests that Scandinavian Christians are a lot like American Jews, who are also highly secularized in belief and practice, have strong communal feelings, and tend to be well-behaved.
American atheists, by contrast, are often left out of community life. The studies that Brooks cites in Gross National Happiness, which find that the religious are happier and more generous then the secular, do not define religious and secular in terms of belief. They define it in terms of religious attendance. It is not hard to see how being left out of one of the dominant modes of American togetherness can have a corrosive effect on morality. As P.Z. Myers, the biologist and prominent atheist, puts it, "[S]cattered individuals who are excluded from communities do not receive the benefits of community, nor do they feel willing to contribute to the communities that exclude them."
The sorry state of American atheists, then, may have nothing to do with their lack of religious belief. It may instead be the result of their outsider status within a highly religious country where many of their fellow citizens, including very vocal ones like Schlessinger, find them immoral and unpatriotic. Religion may not poison everything, but it deserves part of the blame for this one.