And yes, belief in the tooth fairy is also based on equal empirical evidence to disbelief. You and I may find that belief silly, but the believer would find disbelief silly too - so who is more right based on the evidence? No one.
You're being intellectually lazy.
Lets take the example of the tooth fairy. We know the claims made by believers in the tooth fairy. They say she comes and replaces lost teeth with money. So, let's see if she does that. When teeth are left alone, the tooth fairy never comes, and cases where teeth are exchanged always involve a humans (usually the parents of the child). If there is a tooth fairy, she doesn't seem to exchange teeth for money (which was her primary descriptive characteristic).
So what else can we learn about the tooth fairy? We can look back in our own history and see that no one referenced the tooth fairy before the 18th century. So if she exists, she may not have always existed. We also know that different cultures tell similar stories about a "tooth mouse" with similar characteristics as the tooth fairy, and that other cultures have completely different traditions.
But we also know that human beings love to create stories about things that don't exist, particularly to delight their children. This is observed behavior of probably every human culture.
We are then faced with a few possibilities. (Try as I might, this may not be an exhaustive list.)
A) The tooth fairy, as a supernatural tooth-exchanging being exists, even though there are no recorded incidents of her exchanging teeth, and she was not apparently known to older or non-European cultures.
B) The tooth fairy is a human story, invented some time in the 18th century. She never actually existed and the stories told about her are the product of fantasy.
C) The stories of the tooth fairy had a basis in history. Perhaps a real-life woman or mouse began stealing teeth in the 18th century. The story was embellished in retellings, since then. No evidence of the historical figure remains.
D) (I'm sure there are other possibilities, so feel free to suggest some.)
What you seem to be misunderstanding, DS, is that most atoothfairyists are not claiming that A is impossible, we're claiming that A is the least likely scenario. B reflects the experiments we do (leaving a tooth) and our understanding of human nature, so we accept it as the most likely explanation of the tooth fairy stories. C and other ideas are interesting, but there's no evidence to suggest they are true (and it's probable that there would be some sort of historical evidence).
There, we've spent the time to look at the situation closely, and rendered a result. That's all atheists do: choose the more likely.