The crucial difference between Santa, the FSM, and some vague notion of gods, of course, is that the latter of the three appears to naturally arise in human beings as a consequence of their illusory "divided self," a remote analogy between the clockwork of nature and the intentional machinations of their handiwork, a sense of moral obligation to some elevated authority, and the ideals of perfection and infinity that practical reason seem to inevitably lead. This is not to say that an idea of a god is true, just that it is natural, and hence makes its comparisons with those other notions utterly superfluous. No doubt Christians and those of the type of faith who believe in a God which regularly intercedes in their own personal lives to save them from minor inconveniences or promises to deal out rewards and punishments for good and bad behavior is entirely comparable to Santa, the God of intelligent persons deserves a more thoughtful rebuttal.
He who loves God cannot endeavour that God should love him in return - Baruch Spinoza