Read this Guardian review and the comments - always read the comments.
Okay, now let me through, I'm a philosopher...
They're talking about religion, and they seem to be doing it at cross-purposes at times. What's a religion? A short answer won't do here, so please indulge me while I suggest a fairly comprehensive answer.
Religions have some or all of the following: 1) a theology, a description of a deity or collection of deities, with or without charming stories about their behaviour, creation myths and tales of their intervention on behalf of a chosen tribe; 2) a set of rules and practices for the worship of that deity or those deities, which usually includes an idea of prayer (don't forget Tibetan prayer wheels!), and of some kind of ceremony which may be private or communal, together with rules and traditions for the practice of that ceremony; 3) a canon law, governing the conduct of its officials, paid or unpaid; 4) a morality, a code of conduct for its followers, which may or may not include the way of treating fellow members and strangers, the role of women, the right or wrong of abortion, sex before, during and outside marriage, and so on and famously so forth; 5) a lifestyle which may or may not include prescriptions and proscriptions on dress, diet, working on a chosen holy day, manner of speech and other such ticks and habits of everyday life; 6) a spiritual practice for dealing with the iniquities, cruelties, tragedies, boredom, frustration, upset, insolence and unfairness of life.
A religion is a theology, a worship, a canon law, morality, lifestyle and spiritual practice. The theology is compulsory, all the rest are optional, even if leaving out a practice of worship would feel a little odd. The faithful may feel that simply listing the pieces out misses something, and indeed it does. It misses the way that religions are claimed to be, and for all I know are actually experienced by their followers as, an indivisible, organic whole.
A totalitarian religion presents these rules, codes and practices as one huge organic whole that must be accepted without question and lived without exception. A more humane totalitarianism allows grades of wrong-doing and a practice of confession and forgiveness. Some religions seem to be about nothing but the lifestyle stuff, others seem to be all about the spirituality, while others are all about the ceremony and community.
Just because someone can't separate rules about the behaviour of women, from the proper manner of prayer or the idea of angels in their religion, doesn't mean that those ideas are not, in logic and in fact, separable. Religious people and even secular commentators who want to sound gruff talk about "cafe religion" or "a la carte belief", with the disapproving air of superiority of those who take their whiskey straight. However difficult it may be for a signed-up practitioner of one or other religion to imagine, and never mind that its management would deny it with loud denunciations, it's fairly clear that each of these six components is quite separable from the other, and indeed many of the items in each can be removed or others added. The result wouldn't be the exact religion we started with, but it would be another religion. The person you're talking to might have difficulty imagining this - "it's not like that, it's all one, it's complicated, you just can't take bits and leave them" - but that's their failure of imagination, not my spiritual emptiness.
What's also clear is that we can have a morality, spiritual practice or a lifestyle without a religion. This is the claim that causes a lot of the dispute, and we need to understand that the dispute isn't about a matter of logic - morality, spiritual practice and lifestyle work perfectly well without theology - but about a matter of feeling: to a paid-up daily worshipper morality without Hell feels a little conventional, spirituality without Heaven feels a little less soft and warm, and of course, lifestyle without God feels totally arbitrary. That's the problem, because it's lifestyle that people are most attached to. The dispute is about them wanting Big Impressive Reasons for not eating pork, not cutting their hair, circumcising the men or killing women who get raped.
When people say that "religion" is a good thing for social cohesion, they are claiming that the mass of the people will follow the morality and lifestyle rules - which is the important bit - all the better for believing in a theology and worshipping. This is a splendid piece of wishful thinking denied by every moment of history and at many places in the present. I think I'd rather live in 21st century Europe where marauding Dukes merely take over each other's companies than in the religious past when the Dukes actually sent soldiers to kill and rape people and burn places down. Losing your job is no picnic, but it's better than being raped or having your arm chopped off.
What do we make of people who say that "religion" is sometimes a Good Thing? First, check if they really are talking about the Pope or The President of the Church (head Mormon). If not, ask them for an example, which will quickly show you if they are really hankering after the morality, the lifestyle or the spiritual practice. If they're after any of these, ask them if they want an Ayatollah and a prohibition on pork on the side? After they have finally understood what it was you just asked them, they will say "no, and what's that got to do with it?". Well, if you want a religion, you have to choose: Pope, Ayatollah, Chief Rabbi, one of those guys, and several of them come with a prohibition of shoes for women on the side. At this point whoever it is will give you a funny look, because they weren't talking about that. It will turn out that they don't really know what they are talking about, but at a push, what they really want is the ceremony. Thursday prayers, facing Mecca, the women upstairs, incense, ending with the Serenity Prayer, before shaking hands with the priest on the way out to an organ voluntary, and a good gossip on the green in front of the church, with selected head-shaking at mothers who can't keep their children quiet and whispers about just who Lula May is seeing of a Tuesday evening down by the bayou. Or something along those lines.
They want the ceremony because they think that a sense of community and shared life goes with it. Well, only in their nostalgic dreams. Such a person isn't a serious student of history, politics, the human condition, or even the last few weeks' news. Try saying this: "Good lord, is that Harry Lime, I must say hello, do excuse me".
The final trick is for the religious person to re-define religion to mean any one of the six items, instead of "theology+worship+other stuff". So I'm religious if I share a chunk of some religion's morality, or don't eat pork, or do a yoga class once a week. That, of course, is just cheating. Religion means God, Bishops (or whoever) and silly exclusionary lifestyle rules that serve as membership badges. I say the Serenity Prayer at the end of AA meetings, but that don't mean I believe in a God, let alone the Archbishop of Canterbury. If you get into a conversation with someone who tries to tell you that you can have religion without God and Bishops, politely finish the conversation (see above) and don't play cards or do business with them either.