"Evil" and "Good" are a dichotomy, and didactic thought tends to lead to Aristotlean emphasis on yes/no, omitting the all-important other options of "Maybe" and "I Don't Know."
I think evil exists, because people exist and we all have that capability.
I think good exists, because people exist and we all have that capability.
I think animals/plants/fungi/algae/bacteria/viruses do not give a flying fuck about good/evil. the world gets along fine without humans and without our ideas of what is good or what is evil.
an animal/plant/fungus/algae/bacteria/virus will kill or wait for death to feed and survive. that is not evil, right? It is the nature of things that life feeds on life.
an animal (dolphins/orcas/cats/dogs/monkees/chimps) will also torture or kill another animal just for fun/entertainment/boredom. Is that evil? How can it be evil if the animal in question is unaware of it's own consciousness, much less the other animals' consciousness?
Humans have forethought, at least a capacity for it that is greater than any other creature we have found. We know what our actions will entail, how they will help or hurt someone. we choose to do good. we choose to do evil. There is not a human alive that has not wished death up[on an enemy or a foe or a hated person. The difference between a "good" human and a "bad" human seems to be that a good human understands the thought is just a thought, and to act upon it is selfish and bad. The "bad" humans will entertain such thoughts and go ahead and plan them and carry them out.
There is very little difference between these two humans. the ony difference is their CHOICE to act.
abusers, molesters, rapists, killers, etc, for the most part, choose to do what they do. That choice, that moment when they decide to actually act upon those desires, is what shows true EVIL.