It is hard to believe that demonic evil does not exist. Anything from this drive to make the sexual exploitation of children legal and socially acceptable, to the Nazis, to the ancient religious cults that sacrificed children - a lot of evil. Surely Hitler was demon-possessed. It does seem like evil forces keep coming up to try to destroy everything. It is a good agnostic question that what is God doing then, if anything? Long books have been written about that, as I am sure you know!
The funny thing is, if you are really an atheist, a true materialist, then you should believe that morality is just something of an accident. It’s just rules that we happened to adopt along the way because they were convenient, and helped keep society running smoothly, and they don’t have any more inherent value or “rightness” than that.
Why is a human sacrificing a child to an idol any more wrong than an animal who devours their own young when they can’t feed them? You can’t make a very good materialist argument that it should be, as far as I can see. Yet even materialists are repulsed by such things at some level, no matter how objective and logical they try to be.