The argument, as I understand it, goes like this: the problem with Darwinian explanations is that they entail a materialistic metaphysics, and that is bad because materialism is incompatible with deeply-held assumptions that are necessary for social functioning and for personal fulfillment. So Darwinism, apart from being false (as it is held to be) is also extremely dangerous.
This argument finds an eloquent expression in the work of C. S. Lewis (esp. Mere Christianity) and a more sophisticated elaboration in Alvin Plantinga's "self-defeater" argument against naturalism. Here I want to present one version of the argument; in subsequent posts I'll begin to examine what I think is wrong with it.
The conundrum of modern atheism is that it is committed to two seemingly incompatible theses: materialism and rationalism. The commitment to the first consists of the premise that only entities that can figure in a physical theory (however broadly construed -- dark energy is in, pixies are out) can count as real. The commitment to the second consists of the premise that the world as encountered in everyday experience is intelligible to human reason. Historically speaking, the commitment to the second premise has required a denial of the first, for we can be assured of the intelligibility of the universe only if there is an Intelligence who was responsible for its creation.
At work here is the following line of argument, very powerful but surely in need of critical examination:
P1: Only a rational agent could produce a structure that could be comprehended by a rational agent.
P2: This structure can be comprehended by a rational agent (namely, us).
C: It was produced by a rational agent (if not us, then God).
The foremost arguments against modern atheism, as seen for example in C.S. Lewis and Alvin Plantinga, are supposed to show that materialism and rationalism are incompatible, so that if one accepts materialism, then one must reject rationalism. Conversely, if one accepts rationalism, then one must reject materialism.
Another way of putting this point is in terms of versions of naturalism. Materialism can be interpreted as metaphysical naturalism: nature, however broadly construed, is all there is. Rationalism can be interpreted as methodological naturalism: the methods of the natural science have priority in adjudicating between competing assertions. The Lewis-Plantinga strategy is to drive a wedge between metaphysical naturalism and methodological naturalism. Thus metaphysical naturalists such as Marx, Nietzsche, and Freud are put to one side, and methodological naturalists such as Quine are put on another. Dembski says of Quine:
Quine, though a naturalist, was not wedded to the methodological and metaphysical naturalism of Van Till. Quine was a pragmatic naturalist. This pragmatism allowed him to entertain the following possibility: "If I saw indirect explanatory benefit in positing sensibilia, possibilia, spirits, a Creator, I would joyfully accord them scientific status too, on a par with such avowedly scientific posits as quarks and black holes. (from "Naturalism; or, Living within One's Means," Dialectica 1995, vol. 49); see Naturalism's Invincible Ignorance
The alleged incompatibility of materialism with rationalism, and so the alleged incoherence of modern atheism, is closely connected with the alleged incompatibility of materialism with morality. As rationalism is an epistemological thesis, and so is concerned with what one ought to believe, so morality concerns what one ought to do. In both cases, then, what is concern is “oughtness” or normativity.
In both science and in morality, in our theoretical and practical lives, we are rational beings; we occupy what Wilfrid Sellars called, “the space of giving and asking for reasons.” So one way of seeing the Lewis-Plantinga objection to modern atheism is to see it as raising a skeptical challenge as to how anything merely material, and so fully describable in terms of deterministic laws, could nevertheless also be capable of normative guidance, whether epistemic or moral.
The prevalence of normativity in human life is so obvious as to seem undeniable. (And even philosophers who seem to deny it, such as Spinoza and Nietzsche, may seem to sneak it in the back door having kicked it out the front.) In any event, I shall simply take for granted the basic distinction between "the realm of law" (what is material/physical) and "the space of reasons" (what is normatively oriented, i.e. science and morality). What I shall deny is that accepting this distinction requires that one reject materialism/metaphysical naturalism. Instead I shall show, in the course of working through some thoughts of John McDowell and Hilary Putnam, just how one can have one's cake and eat it, too.