Argument is irrelevant
One argument Martin suggests is more of a statement. He claims that by classing certain theological beliefs as basic one puts those beliefs beyond rational appraisal. Once a belief is declared basic, one cannot rationally evaluate it.
This objection is incorrect. As noted above, a belief is properly basic only if no defeaters are forthcoming for it. Consequently, the belief is not immune to argument. Sceptics could offer rebutting defeaters of theological beliefs, give arguments to the claim that theism is false or they could argue that the concept of God is incoherent or inconsistent. Further, sceptics could offer undercutting defeaters that the grounds that produce theological beliefs are questionable. The assessment of such objections would be vital to determining the rationality of belief in God.
There are further ways sceptics and believers can engage in dialogue. One could point out inconsistencies or incoherence in a person’s belief set, even if one does not accept the beliefs in question. One can grant a proposition held by one’s opponents for the sake of argument and then point out its implications, show that these implications or the beliefs themselves entail things that the person themself rejects or considers absurd. Further, one can show that the views one person holds follow from beliefs his opponent holds and so his opponent has good reasons for accepting these beliefs and so on.
Finally, as I noted above properly basic beliefs are foundational beliefs. A foundation needs to be able to support the structure which is built upon it. One important question, then, is to ask what happens if you take a belief as basic, can one reason from it to find plausible, coherent and defensible answers to the various existential and philosophical questions that we use basic beliefs to assist us in answering. C S Lewis put the point well when he stated, “I believe the sun has risen, not because I can see the sun, but because with it I can see everything else.”
The Great Pumpkin
Perhaps the most common objection to Christians taking belief in God as properly basic belief is what is called “the Great Pumpkin objection.” Plantinga himself cites this argument,
If belief in God is properly basic, why cannot just any belief be properly basic? Could we not say the same for any bizarre aberration we think of? What about voodoo or astrology? What about the belief that the Great Pumpkin returns every Halloween? Could I properly take that as basic? Suppose I believe that if I flap my arms with sufficient vigour, I can take off and fly around the room; could I defend myself against the charge of irrationality by claiming this belief is basic? If we say belief in God is properly basic, will we not be committed to holding that just anything, or nearly anything, can be properly taken as basic, thus throwing wide the gates to irrationalism and superstition?[Emphasis added]
(1) “God exists” is a properly basic belief for Christians. (assumption for reductio)
(2) If “God exists” is a properly basic belief for Christians, then innumerable patently irrational beliefs are properly basic for the groups that endorse them.
(3) Innumerable patently irrational beliefs are properly basic for the groups that endorse them. (from 1 and 2 by modus ponens)
(4) But this is absurd.
(5) Therefore: The assumption “God exists’ is a properly basic belief for Christians” must be rejected.
Turning to (2), Parsons suggests that for any argument used by a Christian to justify the claim that belief in God is properly basic there exists an analogous argument for patently irrational beliefs. This, however, is mistaken. I noted above that basic beliefs, even ones that entail the existence of God, are properly basic in certain circumstances. First, they were typically based on grounds, either perceptual or doxastic. Second, they were justified only if there exists no defeaters for them.
Patently irrational beliefs do not meet these criteria. The reason Parsons’ appeals to patently irrational beliefs is because anyone can see on reflection that they are absurd. But if one can see that a belief is absurd then it is unlikely that it will be a belief that seems true to that person. Moreover, if it is obviously absurd then there exists a defeater for it. One will see that it entails an obviously absurd conclusion; itself.
If we turn to premise (4) another problem arises. Parsons takes it as absurd that a “patently irrational belief” can be rational. This is true if the word “rational” is used in the same sense both times it occurs in this statement. It is not true if the word “rational” is used in different senses. It is not absurd for a belief to be irrational in one sense and yet rational in another sense.
We need to ask, then, what sense of rational Parsons has in mind. Now in order for his argument to follow from (1), the word “rational” must be used in an internalist sense. This is because that is how the term is used by Plantinga when he argues that, in specific circumstances, belief in God can be properly basic.
The problem is that in this sense it is not clear that the claim that the kind of beliefs Parsons refers to are always irrational. Take an example Parsons himself cites, Voodoo. Suppose that a person suffers from some mental disorder which causes her to hallucinate and have a vivid experience, such that, it seems obvious to her that Voodoo is true. Moreover, suppose further, that she has no reason to doubt this experience. She is not aware it is a hallucination and is not aware of an argument against the truth of what she perceives. It seems clear that such a person is rational in the internalist sense, she is not acting irresponsibly given the information available to her. Of course her belief is irrational in an externalist sense, it is caused by brain disorder; and hence, is based on an unreliable process. But this externalist sense is not the sense Plantinga uses when he argues that belief in God is rational in the absence of evidence.
Perhaps Parsons means to use rational in the externalist sense and his position is that it is absurd to claim that Voodoo could ever be rational in this sense; only a person suffering from a hallucination or mental impairment could actually have experiences such that Voodoo was obvious and fail to see the force of argument. If this is what Parsons means then (4) may well be true, the problem now is that it is false to suggest that an analogue of Plantinga’s argument shows that Voodoo is rational. Plantinga argued that a basic belief in God is externally rational only if it is based on reliable ground and a hallucination is not a reliable ground.
I have argued that the rationalist position, that belief in God is irrational in the absence of proof, is incoherent. I have sketched a way of looking at faith and reason under which one is rational in believing in God independently of proof and have defended it against two objections.
Let me finish by citing from Alvin Plantinga's famous advice to Christian philosophers,
We come to philosophy with a range of opinions about the world and humankind and the place of the latter in the former; and in philosophy we think about these matters, systematically articulate our views, put together and relate our views on diverse topics, and deepen our views by finding unexpected interconnections and by discovering and answering unanticipated questions. Of course we may come to change our minds by virtue of philosophical endeavor; we may discover incompatibilities or other infelicities. But we come to philosophy with prephilosophical opinions; we can do no other. And the point is: the Christian has as much right to his prephilosophical opinions, as others have to theirs. He needn't try first to 'prove' them from propositions accepted by, say, the bulk of the non-Christian philosophical community; and if they are widely rejected as naive, or pre-scientific, or primitive, or unworthy of "man come of age," that is nothing whatever against them. Of course if there were genuine and substantial arguments against them from premises that have some legitimate claim on the Christian philosopher, then he would have a problem; he would have to make some kind of change somewhere. But in the absence of such arguments-and the absence of such arguments is evident-the Christian philosophical community, quite properly starts, in philosophy, from what it believes.
 Plantinga “Reason and Belief in God” 74.
 Keith Parsons “Some Contemporary Theistic Arguments” The Cambridge Companion to Atheism ed Michael Martin (Cambridge: Cambridge University Press, 2007) 108.
 Alvin Plantinga “Advice to Christian Philosophers” Faith and Philosophy: Journal of the Society of Christian Philosophers vol. 1:3, 253-271 available online http://www.faithandphilosophy.com/article_advice.php
Belief without Proof: Is Belief in God Rational if there is no Evidence? Part I
Belief without Proof: Is Belief in God Rational if there is no Evidence? Part II