I think you've missed the point. It's illogical to say that there is or isn't a God because no experiment could be done to prove either opinion. The tooth fairy, however, does operate within our Universe and therefore within the laws of science. Therefore, measurements can be done to specifically rule out the concept of the tooth fairy (eg. seeing your parents take the tooth).
If a hypothesis cannot be tested then it is not a valid theory. Therefore, it is not logical nor constructive to have an opinion regarding it.