Yesterday, my wife and I happened into (separate) conversations with religious apologists. My wife's interaction was, she reports, a little heated; my own was very polite on both sides. My apologist tried out the First Cause argument, the argument from the Meaning of Life, and the argument from morality. Having discussed these arguments for nearly a decade, I didn't learn anything new, nor was I persuaded.
What really struck me is how differently religious people think, at least about religion. Religious people take philosophical, syllogistic arguments seriously; skeptics and scientists do not: they take evidentiary arguments seriously.
A syllogistic arguments deduces a conclusion from premises. The canonical example is:
P1: Socrates is a man
P2: All men are mortal
C: Socrates is mortal
The evidentiary argument instead supports or falsifies hypotheses on the basis of the correspondence or incompatibility between a prediction and an observation.
H: All people are mortal
P: If some people were immortal, we would observe them living a long time
O: We observe all people dying before they live a long time
C: They hypothesis that all men are mortal is supported by observation
H: Substances (such as wood) contain a material that, when burning, is converted to heat
P: If such a material exists, the mass of a burned item should be less than it was unburned
O: The mass of a burned substance is greater than the mass of the unburned substance
C: The hypothesis that substances contain some material that is converted to heat is falsified by observation
The disadvantage — well, one disadvantage — of evidentiary arguments is that the hypotheses "underdetermine" the prediction: There are infinitely many theories (sets of hypothetical statements) that would logically entail the same prediction. For example, some immortal people might exist, but they pretend to die or disappear before their long life can be observed.
While evidentiary arguments are problematic, interesting and lucrative to professional philosophers, syllogistic arguments have a much more severe problem: the justification of the premises: by definition we can't justify our fundamental premises syllogistically. They're just sort of sitting there. The only individual "premises" we can justify logically, i.e. those that do not cause a contradiction, are the rules of logic themselves. The best we can do with pure logic is determine whether two or more premises are mutually contradictory: not much of a constraint.
When a believer hears a syllogistic argument in favor of his position, he seems to think, "Hm, the premises sound plausible, they lead to the conclusion I favor; the argument seems good," and stops thinking. The skeptic immediately thinks, "Hm. What follows if we deny the premises? What alternatives are possible?"
Consider the First Cause argument:
P1: Everything that begins to exist has a cause
P2: The (physical, observable) universe began to exist
C: The universe has a cause
Both of the premises seem intuitively obvious; it seems perverse and obtuse to deny them. Indeed, advocates claim that because the premises are intuitively obvious, it is up to the opposition to decisively disprove them.
But obviousness is just not good enough for the skeptic, even as a starting point. Does everything that begins to exist have a cause? Did the universe really begin to exist? And what precisely do we mean by "begin to exist"? For the skeptic, just that such questions can be posed is enough to raise reasonable doubt that the advocate must answer. Without such answers, the conclusion is not proven false, but we conclude the argument fails to prove anything.
These premises seem obvious and undeniable; when they're questioned, theists throw their hands up in the air and accuse the skeptic of dishonest obtusity, of (in the words of my apologist conversationalist) "wriggling out" of the argument, or of pure epistemic nihilism.
The skeptic's position is definitely not epistemic nihilism, since we propose an alternative epistemology, i.e. evidentiary arguments. As to obtusity or bad faith, well, the premises are the only interesting thing about syllogistic arguments, so they naturally draw our attention. It's definitely true that the premises cannot be justified syllogistically. And we know that while our intuition is often correct, it is often enough incorrect (at least on evidentiary grounds) that we cannot rely uncritically on intuition. (And if we do accept intuitive obviousness uncritically, I find it intuitively obvious that no god exists; it is the theist who is being obtuse by denying this obvious premise.)
I spent about 45 minutes with my apologist examining the premises of his arguments (and I did manage to get him to agree that meta-ethical subjective relativism was at least coherent); he became increasingly frustrated (but unfailingly polite) with what I'm sure he saw as my own obtusity at refusing to accept what were to him obvious and unquestionable premises. Using my exceptional powers of 20-20 hindsight, I really wish I'd said to him, "We think differently about the world: to me, that some premise seems obvious makes it less plausible, subject to more scrutiny, than a premise that seems controversial and counter-intuitive. When a premise is counter-intuitive, we unconsciously look to an evidentiary justification; when a premise seems obvious, we are likely to take it for granted without considering the evidence. Skeptics are, if anything, more skeptical of the seemingly obvious. That may seem obtuse to you, but it seems obtuse only because our minds are operating along different tracks, at least with regard to arguments for the existence of God."