Scientists and atheists tend to be naturalists. Owen Flanagan, a professor of philosophy at Duke University, has written an article titled Buddhism Without the Hocus-Pocus in a recent issue of The Chronicle of Higher Education (January 13, 2012, page B4, unfortunately behind a subscription wall) which provides as good a definition of naturalism as any.
Naturalism comes in many varieties, but the entry-level union card—the famous empiricist David Hume is our hero—expresses solidarity with this motto: “Just say no to the supernatural.” Rebirths, heavens, hells, creator gods, teams of gods, village demons, miracles, and divine retribution in the form of plagues, earthquakes, and tsunamis are things naturalists don’t believe in. What there is, and all there is, is natural stuff, and everything that happens has some set of natural causes that produce it—although we may not be able to figure out what those causes are, or were.
Why be a naturalist? World historical evidence suggests that naturalism, vague as it is, keeps being vindicated, while the zones “explained” by the supernatural get smaller everyday. Naturalism is a good bet.
The more sophisticated religious people realize that the supernatural is getting steadily squeezed out and they often make the case that all the magical and supernatural elements of religion that run counter to science are not what gives their religion its value and can be dispensed with. Rather they claim that it is the moral and ethical teachings that the religious texts espouse that are central to the religion. I hear this claim all the time in the circles that I move in.
But can religions really be drained of all the magical and supernatural elements and still retain any coherence? If you systematically eliminated the hocus-pocus from the religious texts of (say) Judaism, Islam, and Christianity, what would be left? In general, it would be a complete mess, with stories, aphorism, and teachings that are all over the place.
You could, of course, comb through the debris and pick out bits and pieces to construct some kind of coherent philosophy but what would be the point? You would, in essence, be using some external philosophy as a template to decide what aspects of that religion were worth saving and what to discard. But if one already has that template at hand, what is the need for those religions at all?