Whether you inhabit religion from the inside, or view it from a cultural distance, surely it is clear in either case that religion is something that changes through time, that the parts of religion that work well tend to spread, and that the parts that work poorly tend to die out.
Why do the religious believe so strongly in the importance of preaching to the masses and proselytizing people? Because this belief is intrinsically good at propagating itself. Religions that don't include this conviction don't spread. They are out-competed. This belief is, biologically speaking, the replication drive.
Why do so many people believe that religious doctrine is sacred and must never be changed? Because this belief is intrinsically good at protecting itself from change. Religions that include this belief are good at maintaining themselves. This is why all religions are protective of their doctrines. They are conservative. If they weren't, they'd die out.
Why do religions promote community? Because religions that help the community offer benefits to people, and benefits help to gain recruits and keep followers.
Belief after belief, each component of a religion is ultimately present for one historical reason: The religion was better able to spread and survive because of it. Darwinian evolution selected for those traits.
Each new person who enters into a religion, whether from the outside or born into it, contains a unique understanding of the religion. These variations among people are inevitable. Of these millions of variant beliefs, across millions of people, some are better able to spread to new recruits than others, and the more successful variants become dominant. As a result, over years, over millennia, a religion becomes honed, shifting, changing, until it is well adapted to survive. A religion is good at spreading, at protecting itself, at fending off other religions, at cozying up to the quirks of human psychology, at tapping human emotion, because any variant of the religion that is weak in those respects is soon out-competed and dies off. New religious flavors, new interpretations, new splinter groups are constantly being formed, remain for a while, and fade away or take over, as they are worse or better at their own spread and survival.
A religion is a life form that grows in the Petri dish of human culture.
The idea that religions are meme structures, and that the evolutionary pressure on them pushes them toward their own benefit and not ours, was proposed by Dawkins (The Selfish Gene) and elaborated by other philosophers of memes including Blackmore (The Meme Machine) and Lynch (Thought Contagion).
This situation with religion is arguably an example of a Nash equilibrium, an equilibrium between two interacting entities that have goals that are not quite identical. In this case, the two entities are the religion itself and the people who comprise it. Religion can never be truly 100 percent in the service of the people because the evolutionary pressure on religion is ultimately to promote itself.
One could even plausibly argue that conservative and liberal religions, or conservative and liberal groups within a religion, represent two distinct but stable mathematical solutions to the Nash equilibrium problem. A conservative religion is more stick than carrot. It has settled on a relatively draconian punishment attitude toward deviance from the core beliefs, thereby protecting itself from dilution. As a down-side, the draconian attitude risks making the religion alienating and unwelcoming, thereby impeding its spread to new recruits. In compromising among the various factors, it has found an equilibrium that places relatively more emphasis on protecting the ideology and relatively less emphasis on the needs of the constituents. It emphasizes both, but one more than the other.
A liberal religion is more carrot than stick. It has settled on a relatively lenient attitude toward variants of the core beliefs, thereby allowing itself to be welcoming to a greater diversity of people. It is better at pulling in recruits. As a down-side, the liberal religion risks dilution of its core beliefs and therefore its own extinction. It has found an equilibrium that places relatively more emphasis on furthering the needs of the constituents and relatively less emphasis on protecting the ideology.
These two strategies, or efficacious compromises, could be understood as distinct, stable solutions to the Nash equilibrium. Just as a guitar string can vibrate at different stable frequencies, so the religious culture might vibrate in different equilibrium states --conservative and liberal. (Conservative and liberal politics, at least in the United States, seem to be mainly carried over from conservative and liberal religious beliefs.)
As an atheist, I guess I am supposed to be anti-religious. Some commentators favor the complete eradication of religion, any religion, all of them, whatever the particular story of creation, or the particular name given to a deity or deities, or the particular set of rituals involved. The most common argument for exterminating religion is that it promotes brutality and intolerance. In startling contradiction, one of the most common arguments for spreading religion is that it promotes moral behavior. I find this question extremely interesting. Should we, as a rational scientific society in the information age, work to eliminate superstition and religion, or work to spread it further? Let the culture wars rage.
To be honest, I am not sure that religiosity is statistically correlated with brutality or decency. I tend to think that people are brutal and decent, selfish and incredibly generous, whatever level of religiosity they may practice. Yes, wars have been fought in the name of religion, but the Soviet Union also did a good job of violent mayhem with an atheistic premise. I remain utterly unconvinced by either argument. I am a scientist and to me the controlled experiments have never been done and the data do not support either contention. As far as I can tell, religion neither causes nor prevents violence, though it tends to come along for the ride either way, and may tend to intensify the emotions. There certainly are examples of religious splinter groups that advocate violence and those that advocate peace.
My main problem with the view that a rational society should eliminate religion, however, has nothing to do with the dangers or merits of religions. I simply think that eradicating religion is not possible. It is a fallacy that ignores the specs of the human machine. We are not rational entities. Religion, like all culture, grows on the social machinery in our brains. To function socially, we must understand each other's minds; therefore we are built to mirror each other's mind states; therefore beliefs and customs spread by imitation from person to person; therefore a cultural competition among beliefs emerges; therefore belief systems evolve to be especially good at promoting themselves. Therefore religion. For that matter, therefore politics. Therefore entertainment. Therefore business. Therefore all of human culture. If religion is profoundly irrational, so is the rest of human culture. Culture is by nature a complicated, bizarre, irrational, fantastic, addictive pleasure, sometimes brutal, sometimes incredibly generous. People being who we are, masters of inconsistency, we are able to be irrational and at the same time intellectually aware of it. We can study the human mind from a scientific point of view and come to a logical understanding of its intrinsically bizarre illogic. To me, that contradiction is one of the most marvelous properties that we humans possess.
This is an excerpt from the book 'God Soul Mind Brain: A Neuroscientist's Reflections on the Spirit World' (Leapfrog Press, 2010) by Michael S. A. Graziano, a professor of neuroscience at Princeton University.