In my experience, self-described naturalists tend to get irritated when you point out that naturalism often functions as a religion. Perhaps it is because they recognize that there is little space between functions as religion and is a religion just as there is little space between functions as a house and is a house.
Granted, for purposes of city property taxes, that garden shed in which you’ve taken up residence may not qualify as a house, but that doesn’t change the fact that it’s the place where you sleep each night: that which functions as your house is your house.
Many naturalists seem to think that because naturalism is not widely recognized as a religion, that it is exempt from functioning as a religion and thereby being a religion. But that’s mistaken. Just as a garden shed can become your house regardless of whether the city recognizes it as such, so naturalism can be your religion.
So how would you know if naturalism was functioning as your religion? Start with this: does naturalism occupy significant overlapping space with that which is typically occupied by religion? For example, religion typically provides an account of the ultimate nature of reality and the means to live rightly in accord with it and to gain knowledge about it. Does naturalism do that?
Well yeah, of course, it does. Naturalists claim that all that exists is one kind of thing which they call nature. They thus explicitly deny the metaphysical claims of many other religious perspectives. In addition, naturalists claim that science provides the one unique authoritative means of inquiry into that one metaphysical reality called nature.
Religions also standardly provide an eschatology — a vision of the future — and that often includes a mixture of hope and stoic resolve. Naturalism does this as well. It’s greatest prophets — folks like Carl Sagan, Richard Dawkins, Neil deGrasse Tyson — wax eloquently about the depth of cosmic time, the prospects of our future existence among the stars, and the staggering finitude of individuals and the collective whole against this vast stellar backdrop.
One key aspect of religion is worship. But we should be careful here because people often think of worship in an overly narrow sense as if it is essentially tied to singing songs in a group, dropping money in a collection plate, and engaging in acts of prayer to a personal deity. Those are token examples of religious acts common in western monotheistic religions, sure, but beware that you don’t confuse token and type. Houses are not limited to those abodes that are charged property tax and acts of worship are not limited to those that consist of acts of piety in western monotheistic religions.
Other religious traditions exhibit their own worshipful practices such as meditative acts of mindfulness oriented toward a transcendent cosmic reality. And anybody who has listened at any length to the above-mentioned prophets will recognize the reverent awe they grant to nature and science looks very much like the reification of worshipfulness to its essence. And once again, if it functions as worship, we should recognize that that is what it is: worship.
So the way I see it, naturalists should go ahead and recognize naturalism for the religion that it is. Continue to praise the potential of science, ruminate on the fleeting mortality of the individual, speculate hopefully of the expansion of our species to the stars, and lapse into silence at the dizzying expanses of the heavens. Embrace your religion for what it is. We won’t judge you, I promise.