God created free will -
Bringing in Satan and his hordes to explain evil and suffering creates more logical problems than it solves.
How could angels, created sinless and capable of remaining so, and in direct, unmediated communion with God, ever come to sin? If we accept for the moment that they did, why didn't God forgive and restore them? Given that God didn't, why didn't God annihilate them, rather than allowing them to continue in an existence of suffering for them and danger for others? Given that God didn't do that, why did God allow Satan and his chums to have any influence over humanity? Given that God did, why did the sin of Adam and Eve infect the rest of us?
These are the logical knots you tie yourself in if you believe in an objectively-existing Satan - or God, for that matter. The early chapters of Genesis, as well as much else in the OT, are so obviously myth and allegory that you've got to be literarily cloth-eared, as well as a scientific troglodyte, to think it's literally true.