I find it interesting that he uses the "add on" that it is too small to see - which is OK in this example as he is arguing that an inability to disprove something is not evidence that something exists. This however is the type of protective strategy that is often employed by religious apologists when their argument is destroyed. They keep adding things on to protect their conclusion when in fact, they should be arguing for their belief.
An example would be the morality argument - you know the one: there is good in the world, therefore god is good (if you allow for him to exist for the sake of argument). You point out gas chambers, genocide and cancer and claim that god is either evil or does not care about human welfare. They now claim god has a purpose, often involving phrases like "free will", so evil is allowed. This of course has no evidence to back it up. It's just an idea created to protect a pre-conceived conclusion. Instead of deriving something of the nature of god (again assuming he exists for the purpose of argument) it becomes a "justification" to protect their viewpoint. A viewpoint that does not stand up to scrutiny. You may then counter that "free will" (if we have it) has nothing to do with things like children being born deformed. A common response to this is that the whole universe is polluted by "sin". Again, this "protects" the belief that god is good, but provides no supporting evidence that "sin" (something I don't believe exists) has polluted everything. So, the believer just heaps more and more unsupported claims on top of each other to protect that which they already "know" to be true because that is what one interpretation of their "holy book" says must be so. The whole thing becomes a convoluted mess, The best that can be hoped for is a consistent theology - just like you can also have consistent fairy tales too.