The existence of evil is difficult to understand if we assume the universe is the product of a perfect God. However, embrace the scientific/evolutionary viewpoint and evil becomes understandable. After all, what is supremely “good” for the ebola virus is extremely “evil” for the primate infected by ebola.
Natural selection provides a framework which enables us to understand why species are so often in conflict with each other. If each species has its own morality or “rightness”, it follows that the result of the evolutionary process is a world of competing moralities.
Evil exists, from the evolutionary perspective, simply because other species exist with their own conflicting needs and rights. Why conflicting? Because there is a limit to resources—so much sunlight, so much oxygen, nutrients, energy resources, and no more. Sometimes, it’s true, one species will develop a symbiotic relationship with another species in situations where the two use resources in a mutually beneficial way. But far more common is conflict.
The simple truth is that species often feed on each other. The delicious meal which is profoundly good and necessary for the wolf is profoundly evil from the lamb’s perspective. This is understandable within the context of natural selection, but not easily explained if there is a perfect God.
Why would a perfect God create a world of such limited resources and resulting competing moralities?* Or, to turn this question around into an even more devastating form for theism: why would the existence of a world of limited resources and competing moralities, be best explained by postulating a perfect God?
The answer, quite simply, is that it wouldn’t.
On the other hand, what is the point or value of postulating an imperfect God? Why would anyone think that better than simply taking science at face value, and therefore not postulating any creator at all?
* Notice that the usual “solution” of blaming evil on human misbehavior doesn’t work here. Human misbehavior doesn’t explain why other species are subjected to evil happenings as well. It fails to account for the existence of competing moralities between species. It doesn’t explain why God created limited resources, or created species which must devour other species to live, or why natural disasters—floods, volcanoes, tornadoes, earthquakes—kill not just misbehaving humans but other animals as well.
Whatever mental gyrations are attempted in order to get around these difficulties, they always seem to leave theism further out on a limb. The result is that the scientific/atheist answer, in contrast, appears far more convincing.
What is a major reason people reject atheism? They reject it because they find it far more appealing to believe that the world is ultimately perfect and ideal. But the absurdities necessary to maintain a claim of universal perfection have the effect of rendering theism even less appealing than atheism.