All the tabloid-fed hysteria, the religious ravings, the pompous and hostile commentaries, made no sense, of course. If to abandon ten or a thousand … - Stephen Baxter

A growing belief that behind every event lay intention—be it an evil thought in the mind of another, or the benevolent whim of a god in the sky—was perhaps inevitable in creatures with an innate understanding of causality. If you were smart enough to make multicomponent tools, you eventually came to believe in gods, the end of all causal chains. There would be costs, of course. In the future, to serve their new gods and shamans, the people would have to sacrifice much: time, wealth, even the right to have children. Sometimes they would even have to lay down their lives. But the payback was that they no longer had to be afraid of dying.

Well, the world may be heading for the iceberg, but the dead hand of old Darwin is still on the tiller.
What am I talking about? Just this: if most people stop breeding, the handful of people who love kids and want to have them—people like me—are, within a generation or two, going to outnumber everyone else. Simple math.
And that’s exactly what is happening.

One might imagine that, in any conflict between rational humans and religious humans, the rational ought to win. After all, it is rationality that invented gunpowder! And yet—at least up to our nineteenth century—the religious tendency has generally won out, and natural selection operated, leaving us with a population of religiously-inclined sheep—it has sometimes seemed to me—capable of being deluded by any smooth-tongued preacher.
The paradox is explained because religion provides a goal for men to fight for. The religious man will soak some bit of “sacred” land with his blood, sacrificing far more than the land’s intrinsic economic or other value.