It seems obvious to me that there are at least two entirely different conceptions of "religion" that various commentators and intellectuals are addressing. It seems puzzling that this distinction is not more widely recognized.
The first sort of religion is religion as truth: The "otherworldly elements" or supernatural explanations of the universe and especially human and social psychology; elements held as real, literal truths. These truths might be revealed only dimly or imperfectly by scripture, but at some level these otherworldly elements are held as no less truthful than any scientific truths, themselves perhaps only dimly and imperfectly illuminated by experiment.
The second sort of religion represents all the rituals, beliefs, ideas, art, literature and most especially "cultural" practices that accrete around the aforementioned otherworldly elements.
It is tempting to simply dismiss the supposed "truthfulness" of the otherworldly elements and simply concentrate on the cultural aspects. Roger Scruton notes that the Enlightenment thinkers, especially Hume, Voltaire, Diderot and Kant, decisively established "the claims of faith to be without rational foundation," and no one since, notably Dawkins and Hitchens, has added anything substantively new.
Scruton is perhaps correct: I personally found in neither The God Delusion nor god is not Great any philosophical arguments that I didn't figure out on my own, and if little ol' me can figure it out, it must have been child's play for the Enlightenment philosophers. But I think the facile dismissal of modern atheist writers that follows from this observation is too hasty for two reasons.
The first reason is, of course, the sheer number of people who actually do consider their scripture to be absolutely literally truthful. Richard Dawkins is a scientist; he wouldn't even be a part of the debate were it not for the considerable political power and influence of Creationists and Intelligent Design proponents. Hundreds of millions of Muslim women live in terrible oppression precisely because Muslims hold the literal truth of the Koran and its prescriptions on the status and role of women. While one can justly note the spiritual dimension of religion, one cannot so blithely claim that religion is viewed by all or even most only in a spiritual sense.
The second reason is that any anthropological study of religion must critically examine the claims of truth of religions' otherworldly elements in relation to the cultural practices of the religious. To simply dismiss as unimportant religions' claims of truth simply because they are patently absurd is to ignore what sets religious cultural practice apart from secular practice. One might just as well try to study the difference between birds and mammals by first dismissing the element of flight as a distinguishing characteristic (indeed it's true that a few birds cannot fly; a few mammals can).
The dismissal of otherworldly truth claims, for instance, renders Wilson's sample study of religion banal and scientifically trivial. Cultural practices are prima facie adaptive, finding that some of those practices happen to fall under the rubric of religion tells us nothing. To learn something about religion we need to carefully study the causal efficacy of the otherworldly elements themselves as well as their belief as truth among the religious. This is precisely the study Wilson doesn't perform; one suspects that Wilson (an atheist) simply hand-waves over this lack precisely because he considers the truth claims unimportant because they are absurd.
Another reason the dismissal is too hasty is that if the absurd truth-claims of literal scripture are simply dismissed as unimportant and irrelevant, the reader is free to establish a "spiritual" authority for a scripture without ever critically examining why any sort of authority would get the facts wrong.
We see this sort of uncritical spiritual authority all over the place: Religion is another way of "knowing". Scruton uncritically declares scripture to be spiritual truth: it is about "what happens always and repeatedly;" "rehearses [the world's] permanent spiritual significance'" quoting Hegel, "the eternal and necessary history of humanity;" and "conveys truths about freedom, about guilt, about man, woman and their relationship, about our relation to nature and mortality." [emphasis added]
But does religious scripture really have any sort of truth content? It's certainly data, it's very interesting, it's often profound literature, but does its content really deserve the sort of authority claimed by those such as Somerville and Scruton, as well as religious "moderates" such as Andrew Sullivan? Why should we grant religious scripture and religious belief any authority over universal spiritual "truths" when it makes claims about factual truths which are blatantly absurd?
I'm willing to grant the possibility that some specifically religious cultural practices are valuable, or that some valuable cultural practices have survived because they were specifically religious. But we cannot make much scientific progress in the study of humanity in general until we get a few things straight: It's not only that the factual truth claims of religion are absurd, but it's also important that these claims are absurd. Religious scripture does not have any kind of authority, spiritual or factual; scripture has no more authority than any other work of fiction, be it Macbeth, Atlas Shrugged or My Little Pony. There is no magical truth in religion, neither factual nor spiritual, neither in practice, belief nor scripture. Whatever knowledge is gleaned from scripture will be the same sort of knowledge gleaned from any work of literary fiction, and gleaned by the same scientific methods as all other knowledge.