Lothar over at lotharlorraine.wordpress.com approvingly points us towards this article concerning the burden of proof by the Evangelical Enrichment Journal. I mentioned negative dogmatism in a recent post so it's worth dipping into.
Second, the atheist also bears the burden of proof in making the claim, “God does not exist.” Keep in mind: The atheist is actually making a claim to knowledge just as the theist is. So rather than shrugging off any burden of proof, the atheist should understand that both claims needs justification, not just the theist’s. If you make a claim to know something, you should be able to justify that claim when challenged. The atheist — if he or she is a true atheist — says that God does not exist. But we can ask, “Why think this? What positive arguments are there for this claim?” To date, there just has not been any argument coming close to showing how this is so. Some might say, “Arguments for God’s existence do not work.” But that is not enough. You need to show why God does not exist (more on this below). In my experience, the “atheist” more often than not turns out to be an agnostic.This is the old 'atheists are really agnostics' move. But why is rejection of the positive argument for God dismissed as "that is not enough" and why is the burden then firmly placed on the atheist to justify a negative dogmatic position under terms defined by the evangelist? Why is rejection not sufficient?
The atheist who rejects the positive argument for God may argue along these lines:
[P] It is rational and responsible to believe a proposition one finds convincing because it is sufficiently supported by reason and evidence.
['P] It is irrational and irresponsible to believe a proposition one does not find convincing because it is insufficiently supported by reason and evidence.
We can interpret these premises as being either normative or causal. Here will I simply note the distinction.
A normative interpretation asserts we should not believe a proposition insufficiently supported by reason and evidence. This is an ethical statement that we sometimes struggle to achieve. The causal interpretation asserts our character or disposition causes us reject an argument we find unconvincing because of poor reasoning and a lack of evidence. It is not a matter of choice or free ill.
Both P] and ['P] can be defended fairly easily at the cost of broadening the conversation.
However most atheists are not especially interested in philosophy. Their primarily concern is the political and social implications of organized religion. So I recommend giving the following cheeky answer when challenged for positive proof of atheism: God does not exist because such a loving God would not allow the continued existence of the Roman Catholic church (replace with relevant sect). This is a twist on the problem of evil and focuses the conversation away from deism towards the social implications of religious authority.