It occurs to me that, in vociferously denying your allegiance to "God" and claiming "Satan" as your personal honcho deity, you are actually reenforcing the existence of the very thing you call a fairy tale. How can a person be so strongly against a thing that doesn't exist? It would be like me saying I deny Cat in the Hat in favor of the dude from Green Eggs and Ham. Makes no sense. If you deny the existence of God, why try so hard to play for "the other side"?
Besides, the concept of God and the Devil was more complex than your simplified version in the above posts. Morningstar per legend was the best and the brightest of the angels, but jealous of God's new toys and he overstepped his authority. Then, when given a chance for redemption, he failed to humble himself and recognize any weaknesses in his own philosophy, unlike Adam who had a similar crisis of arrogance but realized his error and was therefore given some form of redemption.
Without recognizing your own shortcomings, you cannot grow. This is Lucifer's ultimate failing, the inability to grow and learn from his own mistakes, that God punishes. God of myth and story WANTS his subordinates to grow: why do you think he put "the tree of knowledge" dead square in the middle of everything, then made strict and dire warnings "Not to touch it"?
Because disobedience for reward is the substance of free will. Any parent knows this basic fact. If Adam and Eve don't disobey, they have not acquired independent thought and the experiment is a failure. That's why God booted them from the garden, saying "Now they are like us."
Capable of thought and self-preservation, and no longer in need of shelter.
Of course, God shows a little of his own insecurites by the whole "worship me first" stuff and the refusal to bestow immortality, but hey. Who's perfect?
Bottom line: it is arrogant to assume that there is an old guy so much higher than us on the evolutionary scale that we can't perceive him, and yet his ONLY reason for existence its to watch our every move.
However, it is even MORE arrogant to assume that humans are the tip of the evolutionary scale. As surely as there is life below us, there is life above. Count on it.