The problem of evil
The topics of this post (all related): evil, pain, suffering, death.
When considering "bad" things (evil, pain, suffering, sin, death), the essential item in the list is "suffering". Without resultant suffering (to oneself or others) evil is not bad, because it's not evil until inflicting the suffering.
(The thoughts in a mass murderer's mind cause them suffering even before deciding to commit the dastardly deed.)
Therefore, only the word "suffering" is needed for badness because it includes:
Ultimately, suffering requires conscious creatures capable of feeling pain: physical, emotional, mental, or psychological. So, therefore, the source of evil ultimately consists in the creating of these kinds of creatures in a universe outside of God's direct control. (Christians want to believe God is in control over every tiniest detail, but this makes him bad or neglectful.)
Suffering can only occur to a conscious creature who is conscious at the time of the suffering. (Can the unconscious mind suffer? Do non-conscious creatures suffer?)
A rock hit with a hammer doesn't suffer. A corpse doesn't suffer. As we travel backwards down the tree of life from humans toward bacteria, I suppose there is a point at which the creatures no longer suffer because their conscious experience no longer includes the ability to suffer (even though they might experience something, such as "being", and even though they respond to the stimuli of being roughly banged around).
So the question is, how can a good God create conscious creatures that suffer?
God is good and beautiful, but there exist conscious creatures who suffer. Therefore, God either: (1) created the universe having these, or (2) created an entity having the power to create these. In either case, God is responsible for the evil and suffering.
Views people have about the problem of evil (how can a good God create, or allow, evil?):
Various explanations proposed for the existence of evil:
Perhaps suffering is a result of a benign super-powerful creator entity who wants to share the utopia of the spiritual realm with created conscious creatures via creating a physical universe. This, without realizing that suffering is inherently built-in to this physical universe — an oops moment. But why would God not educate these super-powerful creator creatures about the side-effects of creating universes having conscious creatures?
The aspects of this universe which cause it to not be a utopia:
This universe seems designed to guarantee pain and suffering, with its limited resources and constant need for living organisms to recharge by killing and eating each other.
People who believe in a good creator God must find a way that he is not responsible for evil and suffering.
Did God create pain, suffering, and evil? Some views:
The standard Christian view is that evil originates in the heart and mind of evil humans having free will. God created the possibility of free-will creatures but has nothing to do with evil itself.
In their desperate attempt to exonerate God, some Christians say that we need suffering because good comes from it; it makes stronger somehow to cope with and survive suffering. But it is horrific to think we need to be tortured to death for some good purpose. And how can we grow and learn if we are tortured to death? And what about animals who get eaten alive?
None of these "explanations" are satisfying. Some would say that the reality of evil destroys any possibility of theism.