Temperament. A pretty good reason to think that the world won’t collapse into dog-eat-dog nihilism should religion die has to do with the inheritable nature of temperament. Psychological studies suggest pretty consistently that temperament drives ideology (such as whether you’re liberal or conservative), and temperament has a substantial genetic component (at least half of your temperamental inclinations can be attributed to your genes).
Bonobo v. chimp. Bonobo-style atheists (a.k.a. hippie humanists) couldn’t consistently be obnoxious Ayn Rand/Nietzsche “bloody chimp” atheists if they tried because the emotional set-point for bonobo atheists is simply not going to let them live their lives like Nietzsche advocated. It’s just not in them to behave that way. Even if bonobo atheists thought (in the abstract) that Nietzsche’s ideas brought one to the correct worldview, it doesn’t follow that they could, in practice, live out their convictions. The same is true for those who are more “chimp-like” and aggressive in temperament: they can’t consistently be made into nonviolent hippie-humanists or Jesus-hippies by argument alone.
Thank the Lord for hypocrisy! Think of contemporary Christians, for example. Very few have the temperament for the degrees of self-sacrifice advocated by Jesus in the gospels (“sell all you have and give it to the poor”; “turn the other cheek”; “always be meek”; “don’t look at those of the opposite sex to lust after them”), and yet Christians say that they agree completely with Jesus. In this case, hypocrisy and cognitive dissonance come to the rescue of what might otherwise prove to be poorly thought-out, unworkable, rash, or extreme behavior.
Likewise with Jesus’s philosophical opposite: Nietzsche. Should an atheist world ever come about, it will largely function in a vaguely liberal and humanist manner even if everyone arrives at the same nihilistic conclusion that Nietzsche was right and has always been right. Regardless of ideology, people will behave in pretty much the manner determined by their temperamental makeup. Barring direct and systematic genetic tinkering with temperament (probably still at least a century away) on scales such as “cooperative v. selfish” “timid v. risk-taking,” and “open v. closed to the pain of others,” etc., there will be pretty much the same mix of human temperaments as there are today. So if religion died tomorrow, we could probably rest assured that the world would go on pretty much as it has always gone on.
This means that hypocrisy is the friend of both the theist and the atheist.
Thank the Lord for cognitive dissonance and evolution! It’s sometimes said by the religious that New Atheists, by largely advocating liberal humanism, are cognitively dissonant about Nietzsche, and that they’re hiding from themselves the true import of their own ideas because they’re being hypocritical and cowardly. But what is being ignored by those who make this critique is that there are good evolutionary reasons, perhaps not wholly conscious to atheists, for advocating humanism. The same is true for the cognitively dissonant theist who emphasizes in religion, say, the behavior of Jesus over the behavior of Abraham (who raised his hand to kill his own son Isaac for no other reason but that God told him to do so). Depending on your angle of vision, cognitive dissonance takes in everyone; it is an equal opportunity employer.
Evolution has come up with two broad strategies for survival–cooperative and go-it alone strategies. If you belong to a tribal species (as we do), the majority of us will be deeply inclined genetically to be “nice” in the majority of circumstances wherever we interact with those we determine to be in our “circle.” Therefore, if religion is not a sufficient buffer to the sorts of nihilism and individualism that some theists warn against, it appears that the “running-in-packs strategy” of our human evolution is.
If we were sharks, it would be different. If we were a species of big-brained sharks, something like Christianity would certainly be needed to check us, for our inclinations would be independent and ravenous in all circumstances. That’s, after all, a shark’s evolutionary strategy. But that’s not the human evolutionary strategy when it is combined with civilization. Absent civilization and primitive tribal cooperation, we are “nasty and brutish” to one another, especially in zero-sum games where resources are in short supply. But, again, these factors are only wholly in play if civilization and primitive temperamental cooperation are lost. And both theist and atheist humanists (thankfully) seem inclined to want to keep the “nasty and brutish scenario” from ever happening (and there are increasingly plenty of non-zero sum games to play in the world based on win-win international trade). So you can have a world without religion as a buffer to the Nietzschean will and still not see the collapse of civic order thanks to already existing civilization, non-zero sum games, and the evolution of temperaments inclined to empathy and cooperation.
What about the existential problem? The above points do not solve the existential problem of meaning for human beings in the way that religion pretends to, but they at least give us good reasons to think that Nietzsche’s “blonde beast” model of human behavior will never become the norm for the world, whether religion continues in it or not.
Conclusion. If the humanist atheist is metaphysically incoherent–a kind of intellectual oxymoron moving about in the world–she is not so within the context of cooperative evolution. She is completely coherent. It is the person who pretends that temperament is readily malleable to argument that is, in fact, being incoherent with reality.