The Santa Claus / Tooth Fairy Argument

In his book Atheism: A Very Short Introduction, Julian Baggini discusses the objection to atheism that it is "too committed to the value of rational explanation." This objection maintains, he says, that atheists are wrong when they say we should disbelieve in "anything we have no rational reason to think exists." According to Baggini, the problem with this objection is that

it open[s] the door to any number of irrational absurdities. For example, if you want to seriously argue that we should believe in things we have no rational reason to think exist, why not believe in the tooth-fairy? (Non-atheists tend to get irritated when atheists invoke entities such as the tooth-fairy and Santa Claus to illustrate the ridiculousness of permitting belief in what is not rational, but such irritation does not comprise a serious counter-argument.)

I understand what Baggini is saying here and think his reasoning is good. But by using the tooth-fairy and Santa Claus as examples, I think he makes his argument seem weaker than it really is.

Believing in a god doesn't necessarily open the door to believing in any absurdity. Some things we have no reason to think exist are much more absurd than others. We have a very good basis for not believing in the tooth-fairy or Santa Claus, since we know that parents are the ones who put money under kids' pillows and presents under Christmas trees. There isn't "room" for such beings in the same way there could be room for certain types of gods.

Baggini could have made his point more persuasively by using "absurdities" that are not as easily disproven as the tooth-fairy and Santa Claus. Alien abductions, for example, or the gods of dead religions.

(cross-posted with minor edits from the Philosophy & Religion discussion board at IMDb)