That theory also exists in my world, however it's nothing but what I said, only with prettier wording. The existence of a God can't be proved in my world, thus the nature of that God can't be proved either, it can just be assumed. Because people turn to the idea of a God in order to find comfort, God is nothing but the embodiment of every good and positive emotion in the world. Eternal bliss, eternal love, eternal happiness, eternal patience, eternal kindness.
However the idea of such a being existing and giving birth to humans leaves to debate why people aren't like that and where does evil and negativity come from. Thus people create the figure of a demon. The idea of them being formerly angels is just to convince themselves that it's natural that good people turn to be bad people, and to support the idea that the origin of everything was God, the pure and good being, instead of the other way around or admitting a balance between both sides.
[A pause.]
People tend to be fairly simple when they think about something they want to use as a scapegoat.
[Voice]
However the idea of such a being existing and giving birth to humans leaves to debate why people aren't like that and where does evil and negativity come from. Thus people create the figure of a demon. The idea of them being formerly angels is just to convince themselves that it's natural that good people turn to be bad people, and to support the idea that the origin of everything was God, the pure and good being, instead of the other way around or admitting a balance between both sides.
[A pause.]
People tend to be fairly simple when they think about something they want to use as a scapegoat.