For the sake of sanity, Atheists default to zero unless extraordinary evidence comes along to argue for putting a one there.

Actually because the world is intelligible, it is counterintuive to assume a zero. The most obvious intuition is that “something” causes what we observe. Now this might not necessarily be true, but it is far from self-evident that the zero is the natural answer. In the absence of any information about the true value, we are not well served by populating a bit field with zeros unless we have pre-existing knowledge of what the true value is likely to be. If we have no idea, we are simply codifying our ignorance by asserting it is “zero for the sake of sanity”. Thus in a database, you do not enter a default value without some good reason to suspect it will be valid in most cases. If you don’t know the value, you leave it null.

So the argument that “of course” it is a saner to leave it a zero begs the question. Now many of the arguments for atheism introduce a social argument: “see how many people have died in religious wars! If we were all atheists we would leave in peace.” But this is self evidently false. The biggest killers of the 20th century were essentially atheist ideologies. So why not leave the entry null?