The main argument made by Nicholas Wade here (and in his book) is that religion is an evolutionary adaptation as opposed to, say, a spandrel- a byproduct of otherwise adaptive faculties used wrongly. Many have postulated that humans have an innate tendency to deduce agency- that is, attribute a will and intelligence to something which in fact acts out of natural forces rather than emotion. A storm, for example, may appear angry to the observers, but correctly understood it is merely the result of blind meteorological forces. It's easy, so goes this theory, to see that gods began- we simply imagined these beings from an otherwise adaptive faculty.
Wade has a not altogether convincing alternative- religion is in fact an adaptive force for "social cohesion". Though this initially seems plausible, I have trouble seeing that there's that much evidence far it to be. Perhaps we have a predisposition toward belief in a higher power, but its difficult to test this: we rather either have the belief drilled into our heads and acquire it, or don't. According to Wade, in the same way we acquire language early in life, it is similarly much easier to come by religion as a child. A much more obvious answer is simply that we are most impressionable as children, and tend to reflect the world-view of our parents and other influences.
Obviously, just because something is adaptive does make it true, indeed, because their are other reasons for such a belief to evolve, it increases our reasons to doubt such a belief. Those who make the "religion is adaptive" argument tend toward an altogether different argument, namely that it shows religion to be a social good. This is problematic, as many things that are adaptive are utterly evil (rape and genocide, come to mind). Nevertheless, Wade does apparently seem to think that the argument that religion is adaptive and the argument that it is good go hand in hand.
From the New York Times review of the Faith Instinct
Wade would probably deny that being adaptive makes any religion better in a non-evolutionary sense than any other. His scientist’s neutrality slips toward the end of the book, however, when he starts making the case for Religion with a capital R. Like Robert Wright in “The Evolution of God,” Wade wants to defend religion from so-called “new atheists” like Richard Dawkins, Daniel Dennett and Christopher Hitchens, who see it as a malignant illusion. In chapters on religion and trade, religion and warfare, religion and nation, and the “ecology” of religion — the way in which religion regulates fertility and population size — Wade argues that our religious disposition can enhance social and national unity, manage scarce resources, even solve the tricky problem of how to get young men to die for the greater good when that’s called for. But Wade also knows that the faith-based preference for the group has engendered genocide, mass suicide and maladaptive cargo cults. Perhaps that is why he declines to draw one inference that proceeds from his arguments: that individual religions can be compared and ranked and, well, approved or disapproved of, since a religion can be good only insofar as it’s useful.
The argument that religion is merely an evolutionary adaptation and clearly socially constructed, yet ought to be encouraged for its social effects seems incredibly Machiavellian. the argument in a nutshell is that this is not true but the masses should believe it, so that they will be more socially cohesive and hence, among other things. Napoleon made the point similarly "Religion is excellent stuff to keep the poor from killing the rich". If it were true that these myths were useful, there might be some sort of argument, but there's little reason to think they are. Take the example of getting people to die in battle. Evidence points toward the secular being over-represented in the military. Even it true that the religious being more willing to fight and die, today technology is far more important than fanaticism. The Taliban and Al Qaeda have shown themselves far more willing to die for their cause, however, the United States is far more powerful because of the weaponry. In the modern world, know how (primarily furnished by secular scientists) trumps fanaticism ten times over.
Beyond this fact, I don't understand why anyone sane would ever recommend religious belief as a way to encouraging military service. I for one would prefer the soldiers stationed in Iraq and Afghanistan to have a secular world-view, rather than be encouraged to see themselves as on a crusade. I think the other alleged "good effects" of religion are probably similar to this. They sound appealing on first blush, but upon examination don't make sense.