I hate to thieve shamelessly, but that's only a general rule. I was so intrigued by a post on Angry Bear on religion that looked into his source material myself. It's a 2005 study from the Journal of Religion and Society about the pervasive (though sometimes unconscious) tendency we have to equate high degrees of religiosity with social health.
Two centuries ago there was relatively little dispute over the existence of God, or the societally beneficial effect of popular belief in a creator. In the twentieth century extensive secularization occurred in western nations, the United States being the only significant exception (Bishop; Bruce; Gill et al.; Sommerville). If religion has receded in some western nations, what is the impact of this unprecedented transformation upon their populations? Theists often assert that popular belief in a creator is instrumental towards providing the moral, ethical and other foundations necessary for a healthy, cohesive society. Many also contend that widespread acceptance of evolution, and/or denial of a creator, is contrary to these goals….
Among the developed democracies absolute belief in God, attendance of religious services and Bible literalism vary over a dozenfold, atheists and agnostics five fold, prayer rates fourfold, and acceptance of evolution almost twofold. Japan, Scandinavia, and France are the most secular nations in the west, the United States is the only prosperous first world nation to retain rates of religiosity otherwise limited to the second and third worlds (Bishop; PEW).
A few hundred years ago rates of homicide were astronomical in Christian Europe and the American colonies (Beeghley; R. Lane). In all secular developed democracies a centuries long-term trend has seen homicide rates drop to historical lows. The especially low rates in the more Catholic European states are statistical noise due to yearly fluctuations incidental to this sample, and are not consistently present in other similar tabulations (Barcley and Tavares). Despite a significant decline from a recent peak in the 1980s (Rosenfeld), the U.S. is the only prosperous democracy that retains high homicide rates, making it a strong outlier in this regard (Beeghley; Doyle, 2000). Similarly, theistic Portugal also has rates of homicides well above the secular developed democracy norm.
Although they are by no means utopias, the populations of secular democracies are clearly able to govern themselves and maintain societal cohesion.
A couple things leap out here. We know from numerous other studies that high levels of religious participation correlate positively with health behaviors in youth (or at least tends to protect against typical teenage destructive behaviors), and we also know that teenagers tend to leave organized religion in droves about the time they get out of high school.
If, in societies that are equally prosperous, high religiosity does not correlate with positive outcomes for adults (and it clearly doesn't, because in the US, many adult 'believers' zealously kill, rape, maim, commit all sorts of sexually dysfunctional acts, and otherwise victimize themselves and others) then what might that suggest? That religion in the form that most people practice it is essentially suited to children and adolescents, but loses its effectiveness with adults? And would this be because of the evolutionary stage of religion itself, or is this a problem inherent in religion for all time?
These aren't rhetorical questions because I don't pretend to know the answers. I've been deeply attracted to religion for most of my life, but even while I was actively involved in it, I found it hard to truly believe a good deal of what was being professed. And so did a lot of other people sitting in the pews.
One thing I know: as Walter Lippmann, whose book "A Preface to Morals" I'm reading, points out: A religion that must be defended and debated is already blighted. Garry Wills said much the same thing in "What Jesus Meant": If you simply cannot accept the (Christian) story as it's presented in the only definitive source of the story that exists, then why bother with it?
It seems that it's all or nothing, logically speaking. But then again, logic has always been the enemy of religion, which is why from Christianity's earliest days, followers were exhorted not to question or probe.