I always try to emphasize that my non-belief is not a doctrine (how can it be?), but the outcome of a rational epistemology. Good critical thinking skills, of course, should not apply exclusively to the supernatural. That's why a lot of non-believers are also skeptics about alternative medicine, psychics, the Illuminati, and whatnot. But if there's one truth about critical thinking, it's that it can easily be compartmentalized. There are some exceptionally smart people who go to great lengths to rationalize absurd beliefs, who fail to apply critical thinking skills to one area or another when, on the whole, they are generally rational individuals. That's why I often like to point out, when I'm accused of painting theists as stupid because I think they adhere to an irrational belief, that Isaac Newton – one of the most brilliant minds that ever lived – spent much of his life as an alchemist. You can be very smart, in general, and very wrong about specific things.