It's widely taught in Satanism. Humans are animals, and Satan represents that more primitive animalistic aspect of man.
Who really brought more woe and suffering to the planet. God destroyed entire cites, the entire world, killed alot of people, cursed tribes, and sent an angel to kill the firstborn of Egypt. God even gave Satan permission to cause the very few instances of suffering and death that was caused by "the devil." Now again I ask you, who brought more suffering upon the world.
I am by no means a satanist, but I can see some truth to the idea of satan not being an actual entity, but being our carnal, earthly nature; that part of us that is at enmity with the heavenly.
But more importantly than that, the truth is THIS: "God" and "satan," are, in fact, ONE. We, as humans, are made in the image of God. We, as humans, have both a heavenly nature and an earthly nature.
At the moment the Eternal ONE created, It was forced to split itself. At that point, in order to have a creation that was lesser than itself, it had to create something imperfect. The very definition of the word "sin," is "to miss the mark.Clearly, creation, in decay and chaos and at enmity with itself, misses the mark.
In order for God to be recognized as God, It had to create something imperfect, something to look up to God. Hence, It (the Eternal ONE Creator God) had to become imperfect itself. At this point, God had to take on His own "earthly nature" that is at enmity against the heavenly.
All things that exist are thoughts of God. Nothing exists that God does not think and has not thought, and this includes satan.
Satan means "accuser." Satan is the part of God's makeup that recognizes sin as sin and demands a judgment for it. Yahsua is the part of God's makeup that shows mercy. All of us a part of God, and are one with God; one with the universe, and one with each other.
The bible, while not openly and blatantly stating this (the bible rarely openly and obviously states ANY deep spiritual truth) does show us that, in fact, God (as we know Yahweh as being expressed in scripture), and satan, are both a makeup of the same entity:
2 Samuel 24
1 Again the anger of the LORD burned against Israel, and he incited David against them, saying, "Go and take a census of Israel and Judah."
1 Chronicles 21
1 Satan rose up against Israel and incited David to take a census of Israel.
Both of these passages refer to the same event. If one verse says "the anger of the LORD" burned against Israel, and the other says "satan" rose up against Israel, then, who or what is satan?
Things are more easily explained when we come to grasp and accept the Oneness of all that is.