The philosopher Anthony Flew made the case for it (“The Presumption of Atheism,” Canadian Journal of Philosophy 2 (1972). Also available here). What is meant by the presumption is that a-theism, non-belief in God, should be the default, unless evidence is produced for God’s existence. Atheism is innocent until proven guilty. Likewise, theism is guilty until proven innocent.
Flew rejected the usual arguments for the presumption (see his paper). Instead he said this:
. . . to accept such a presumption is to adopt a policy. And policies have to be assessed by reference to the aims of those for whom they are suggested. . . . What then are the aims by reference to which an atheist presumption might be justified? One key word in the answer, if not the key word, must be ‘knowledge’. The context for which such a policy is proposed is that of inquiry about the existence of God; and the object of the exercise is, presumably, to discover whether it is possible to establish that the word ‘God’ does in fact have application. Now to establish must here be either to show that you know or to come to know. . . If a true belief is to achieve this more elevated status, then the believer has to be properly warranted so to believe. He must, that is, be in a position to know.
So basically his case is that placing a burden of proof on theists is the best policy given our goal of knowledge. Knowledge requires evidence.
Two things can be said here. One is that knowledge may not always require evidence. The philosopher Alvin Plantinga has argued for his notion of basic beliefs; beliefs that are warranted because any properly functioning mind would automatically believe them (other basic beliefs: the belief that our senses and reason are generally reliable).
But here is another: what if the goal of belief isn’t always knowledge? Consider the context of personal relationships, we trust our spouses and friends, typically. Have they always produced evidence for their trustworthiness? I submit that this isn’t always the case. Many times there are gaps in our knowledge of our friends and relatives that permit their wrong doing without our knowing. Still, we give them the benefit of the doubt — we trust them unless they do something to violate our trust.
William James argued for so much in his Will to Believe. There he responded to W.K. Clifford’s claim that one shouldn’t ever believe anything on insufficient evidence. Part of his response was that this approach might work well for things on which we have the luxury to wait and gather evidence; scientific beliefs are usually like this. Science is a great place, given its goals, to be an evidentialist like Clifford. But not all situations are scientific situations. Personal relationships involve contexts where one cannot wait on or demand evidence for belief. We have to take risks to have relationships. I figure most people would agree with James that the contexts involving belief in God are more like personal relationships than scientific investigations.
A clarification: belief could mean what philosophers mean by it — a willingness to assert that a proposition is true, and act on it. But Christianity doesn’t have such a flat notion of belief. It’s more like the trust found in personal relationships. Maybe the philosopher’s (and scientist’s) belief is geared toward knowledge. But that’s not the only kind of belief. Knowledge, on the philosopher’s view, is justified true belief (pardon some of the bizarre exceptions). But maybe there is another sort of knowledge found in personal relationships; an intimacy perhaps. It’s no accident that the ol’ King James Version refers to sex as ‘knowing’ someone.
So maybe the best policy isn’t to adopt a presumption of atheism if one’s goals are to have a relationship with God, and not the increase of the philosopher’s (and scientist’s) notion of knowledge. If we want to be friends and lovers of God (as opposed to mere examiners of God), maybe we need to give Him the benefit of the doubt regarding His goodness, or even His existence.