My personal theory, which is as plausible and unprovable as any other, is that a
religious sense exists as a consequence of the evolutionary process. Over
millions of years hominids with larger brains were favored due to their improved
ability to interact socially, communicate linguistically, and obtain food. As
computational power expanded, these same brains incidentally acquired the
ability to grasp their loneliness in the larger world and to anticipate their own deaths. Those who could not imagine a purpose for living turned to less purposeful lives and were marginally less likely to survive to reproductive age, or even to be interested in reproduction. As people without purpose were weeded out of the gene pool, increasingly large percentages of the surviving population were capable of turning their powerful minds to thoughts of gods, whose “existence” would itself become the purpose of life. Man became an animal that could no longer “live in a world it is unable to understand.”
What is almost ludicrous about this theory is Gabel's implied claim that religion ought to be eliminated from human society. Religion, Gabel apparently thinks, is a bad thing and we would be better off without it. Though religion is "built-in" to our species by evolution, Gabel points to examples of people who resist certain natural impulses (e.g., priests and nuns who make vows of celibacy) to show that, if we value rationality and humanism, we "can overcome a natural religious tendency."
But if religion is really hardwired into us as a survival mechanism, why would or should we wish it to be eradicated any more than we (including Gabel, I suppose) would want to eradicate our sexual desires? If religion contributes to survival, then why not keep it around? Indeed, if most people still "feel the need" for religion, then it probably, on Gabel's theory, is still performing a survival function at least for those people--and on evolutionary grounds that would be a good thing (insofar as athiests can talk coherently about "good" and "bad").
Perhaps Gabel thinks that religion has outlived its usefulness as a survival mechanism; perhaps he might point to religious oppression in the world (Inquisition, Crusades, etc.) to show that religion is now harmful, not benificial. Now rationality and humanism are better suited to our survival. But, why should we believe that? Why can't we see even religious oppression as part of the survival mechanism inherent in religion per se?--people have an innate impulse to defend their religious convictions when they feel them threatened because in their genes is an unconscious "awareness" that religion is necessary for human survival. (I'm not advocating this view, just arguing that there is no reason why Gabel's own theory shouldn't lead to this conclusion rather than the one he would likely draw.)
Would Gabel claim that there is something inherently immoral about religious oppression? It's hard to see how he could say that on his own principles. Neither can he say that rationality and humanism are somehow morally better ways for us to live. His only argument will have to be a pragmatic one, one that shows that religion doesn't contribute to survival as well as some other mechanism. But, I think he would be hard pressed to prove that.