Everyone Could Believe In God
In its crude form, the argument from widespread knowledge points to the popularity of religion around the world, usually attributing this belief to an innate, God-created intuition. Anthropologically speaking, this is a weak claim (even without getting into the question of alternative explanations for why people might believe something independent of its correctness). Large portions of the world's population adhere to non-theistic religions/philosophies -- Buddhism, Confucianism, Taoism, etc. The crude argument from widespread knowledge is especially unfavorable to Christianity, as the idea of a single, transcendent, perfect God is not the obvious favorite -- rather, some sort of polytheism or animism featuring many imminent imperfect supernatural beings seems to be the most common outlook. Even people who nominally adhere to a monotheistic or atheistic religion often reconfigure it into a more animist or polytheist mode (just look at how many lay Christians think about angels or the saints).
Alexander Pruss puts the argument from widespread knowledge in a more philosophical form*:
|Every adult who has at least average intelligence, is in at least normal epistemic circumstances (no brainwashing, for instance, and no living in a vat), and strives to figure out the Big Questions with intellectual honesty and openness to truth, practicing the intellectual virtues, putting in an amount of effort proportionate to the importance of the questions and having a firm resolve to strive to live by the truth should he find it, howsoever demanding that might be, will at some point conclude that God exists.|
He spends most of his post dealing with the obvious rebuttal: the presence of thoughtful atheists. He has two major replies, both of which strike me as question-begging.
First is the claim that those atheists can be explained away as not having thought properly about the issue. Obviously they would present no challenge if they did not meet the epistemic criteria set out in the first premise. But to make this argument, you would need to actually show, in the case of any atheist presented as a falsifying case, that that person had made some identifiable error in reasoning. Or you need some general argument showing that atheism can only be arrived at through flawed reasoning. The conlcusion they reach ("there is no God") cannot by itself be evidence of flawed reasoning if you're then going to turn around and use the fact that all non-flawed reasoning concludes that God exists as an argument for God's existence. (You would additionally have to show that some significant portion of the people who conclude that God does exist are not making any errors in reasoning.)
Second, Pruss claims that maybe all those atheists actually have deathbed conversions. He has no evidence for this, other than his faith that God would do that kind of thing. So yes, if God exists, then he might induce us all eventually to believe in him (even if he, for no discernable reason, waits until the last moment so that for all anyone else knows, we die atheists). But that conditional gives no positive reason to believe that God does in fact exist and alter people's beliefs. If we need the deathbed conversions hypothesis to make the argument from widespread knowledge work, then we have to assume God's existence before we can even start the argument meant to support that claim.
Both of these considerations about atheists ultimately lead to the conclusion that Pruss's version of the argument from widespread knowledge is extraneous. That is, in order to make this argument work, you need to introduce some other argument for the existence of God. But then that other argument ends up doing all the work. We could cut to the chase and just make the other argument, without the additional assertion that anyone else who heard that argument would also come to agree with it. After all, if all those people are properly concluding that God exists, they must be doing so for some reason -- a reason that could be offered to the skeptic directly, rather than asking him or her to just trust all of those other thinkers.
The fatal flaw in the argument from widespread knowledge is its democratic nature -- that is, its claim that anyone who thought seriously about the issue would conclude that God exists. The argument from widespread knowledge is a form of the argument from authority. The argument from authority is valid if the authority whose word you're taking arrived at their belief through a process that you would agree is epsitemologically valid. The argument from authority is non-extraneous only insofar as the belief-creating process in question can be evaluated but not accessed by the person who is to accept the belief on the basis of authority. Scientific claims such as the theory of relativity are a good example of a case in which the argument from authority is useful. I can evaluate the epistemological validity of the process by which scientists derive their findings, based on my knowledge of the scientific method and of the ways that the institutions of scientific research enforce compliance with that method. However, I lack the training, eqiupment, funding, and time to personally replicate physicists' discovery process. Thus I can believe in the theory of relativity on the basis of authority. (I should note here that authority-based beliefs are always provisional, since the very esotericism of the underlying claim-validating methodology means that we can't be certain that future improvements in esoteric methodology might not lead to alterations in the authorities' beliefs.) Pruss's argument for God, on the other hand, is democratic -- it holds that anyone can personally recaptiulate the process leading to belief in God. So not only is the argument from widespread knowledge extraneous at the philosophical level due to being parasitic on other arguments (just like the argument from authority with respect to the theory of relativity is extraneous on the philosophical level due to being parasitic on the arguments presented in papers by Einstein and other physicists), it's also extraneous at the practical layperson's level.
Through all of this I've been assuming that the source of belief in God is rational arguments accessible to any serious-minded person. But Pruss's description of the deathbed conversions (as well as a common formulation of salvation by grace through belief) would hold that it's not reasons, but the direct intervention of the Holy Spirit, that causes belief in God. If this is the case, then the argument from widespread knowledge can be reformulated as an argument from authority, because only a few people with God-induced beliefs would need to be found in order to show that God does exist. However, this non-democratic version founders on the question of the epistemological validity of the ostensible authorities' beliefs. How is a person who has not been blessed by directly-God-induced belief to be certain that the authorites really were touched by the Holy Spirit? There may be a perfectly secular explanation of the source of their belief, or it may be a false belief caused by a different supernatural being (e.g. Loki decided it would be funny to make a bunch of people believe in Yahweh).
*Looking back at Pruss's post after writing this, I realize that he's making a more modest claim than I initially attributed to him -- he's rebutting the atheists' argument from divine hiddenness ("God doesn't exist because if he did, he'd make sure everybody knew it"), rather than proposing a positive argument for God's existence. Nevertheless, I think it fails as a rebuttal to divine hiddenness for the same reasons it fails as a positive argument -- to show that God is not in fact hidden, we have to show that everyone does or could come to believe in him, but to do that we have to have an independent argument for God's existence.