First lets throw some light on the concepts of good, bad and evil. What we call as good is when one party irrespective of his own agenda chooses to do things that can benefit others or refrains from doing things that can harm others. Opposite of this behavior is bad and the extreme opposite being evil. But why is being good, good for us? Simply because when everyone behaves the same way, we can expect less destructive behavior from our peers and can live in harmony.

But are we supposed to live in harmony? Evolution, the force behind our existence, requires every life form to prove its fitness by maximizing its access to resources and competing with every other life form. The best strategy to maximize ones access would be to share when confronted with an equal contender and dominate others. Since no two life forms are equal (genetic variation) there are partnerships when apt, exploitation when possible and all the corner cases of evil playing out now and then. Just as expected.

The indoctrination of good, bad and evil by means of culture, religion, law, etc. tries to minimize this phenomenon for a sustainable society. But however hard we try evolutionary forces still reign supreme. We are just another milestone in the evolution of life and are meant to be superseded by better beings just like monkeys before us and the countless many before them. This is the way of nature!