Good vs Evil.....does the existence of God prove the existence of Satan?
First we would have prove the existence of god and the question would then answer itself.
Until that happens we are left to ponder the results of positive and negative behaviour. What we think is off as beneficial to us personaly we lable good. And what we perceive as harmful we lable bad.
Good and evil are simply concepts that are used to define the effect that peoples behaviour has on us or those we care about or identify with. Or what benefits us as a race of people or the human race as a whole.
Good and evil are largely subjective terms that have no value without context. The idea of an invisible mystical creature roaming the earth trying to harm people is a trick of the mind. But then the mind is not entirely rational.