By “atheists” the Order of St. Nick appears to be specifically referring to people from the Richard Dawkins and Sam Harris vein of atheism, people whom I shall refer to as Darwinian Atheists for lack of a better term. Darwinian Atheists are individuals who argue that the Theory of Evolution as proposed by 19th-Century naturalist Sir Charles Darwin disproves the existence of God, by providing a completely natural explanation for the origins of life on Earth. In fact, seven out of the eight cards in the Order of St. Nick’s “Atheist Christmas Cards” collection either reference Sir Charles Darwin or the Theory of Evolution directly.
Though atheism in and of itself is actually a form of religious belief – many eastern religions like Buddhism and Taoism are atheistic in that the belief/worship of a deity is not a mandatory requirement of a devotee – Darwinian Evolutionists deny/refuse to allow their “beliefs” be categorized as such. In fact, Sam Harris in his book Letters to a Christian Nation (2006) even goes so far as to arrogantly declare that "atheism is not a philosophy, not a worldview…it is simply the way things are."
Nevertheless, while the jury may still be out on whether or not atheists of the Dawkins and Harris variety constitute a “religion” the introduction of atheist Christmas cards – such as the one above which depicts Darwin as Santa – in addition to such things as Darwin Fish magnets and the formation of an official Darwin Day holiday (2/12) only help to further the case for some scholars that, at the very least, Sir Charles Darwin is on the way to becoming a mythical, quasi-religious figure.