The theory of satan disproves the theory of god
If satan exists, then god isn't all-powerful, for he would have destroyed him already
If satan doesn't exist, then god isn't pure, for he is causing all the wrongs in the world
If god made satan as a counter-part, then god isn't wise, for he has decided it wrong for the people he supposedly loves to have a perfect existance just because he wanted us to know what good is. although he wouldn't know the difference because evil would have never existed and we would have constantly been content or happy.
Hence, their 'evil' has allowed us to distroy their 'good'
Feel free to apply this to any religion that has only good gods