Even if the omniscient, omnipotent, omnibenevolent God of Christianity does not exist, that does not mean that there is no God at all. We cannot fully comprehend God, therefore we cannot be completely sure that He possesses or does not possess certain qualities (such as omnipotence, omniscience, and omnibenevolence). Thus, any argument that attacks these qualities in an attempt to disprove the existence of God is ultimately irrelevant, since we do not know if God has these qualities or not. However, I believe in the Christian God, so my arguments will defend the existence of the omniscient, omnipotent, omnibenevolent God of Christianity.
Some atheists have maintained that the existence of evil makes the existence of God improbable. But the existence of evil does not negate the existence of God. If God is evil then the existence of evil makes the existence of God even more probable. However, I do not believe that God is evil; I believe that God is good. If God is good, then why is there evil in the world? The answer is 'Free Will' or 'Choice'. God allows human beings to have the freedom to choose between good and evil, and the choices a person makes can affect others as well as himself. Wars can be caused by the evil actions of a few individuals, but many will suffer the consequences. God even gives people the choice of obeying Him or not. God has revealed His will to mankind, and when people follow it great good is the ultimate result. But when people act in ways outside the will of God, great evil and suffering is the ultimate result.
For God to create beings in His own image, that are capable of sustaining a personal relationship with Him, they must be beings that are capable of freely loving Him and following His will without coercion. Love or obedience on any other basis would not be love or obedience at all, but mere compliance. But creatures that are free to love God must also be free to hate or ignore Him. Creatures that are free to follow His will must also be free to reject it. Thus, we conclude that God is capable of destroying evil, but not without destroying human freedom, or a world in which free creatures can function.
Some people think that they can imagine a world where creatures have free will but have no possibility of doing evil. I cannot. If one does not have the choice of doing evil then one does not completely have free will. I can choose to love someone or choose to respect someone, both being good things. I have the ability to choose to do one or the other. But unless I am able to choose to hate that person as well as love or respect them, then I do not truly have free will. If I cannot choose to hate that person then I do not have every choice available, thus I do not completely have free will. To completely have free will, I must be able to make an evil choice (to hate the person) as well as good choices (to love or respect the person).
If the existence of evil makes the existence of God improbable, then wouldn't the existence of good make the existence of God probable? The existence of evil makes the existence of Satan probable, not the existence of God improbable. There is evil in the world because there is a completely evil being that constantly causes suffering and pain. Satan influences people to do evil, thus people commit evil acts and many suffer as a consequence of those evil acts.
Not a great deal is known about animal evil, but it is obvious that some animals suffer because of evil acts committed against them. Man has the ability to choose between good and evil, and he has the choice of helping or harming other species as well as his own. Thus, some animal suffering is caused by humans. God gives animals free will also, and many times they use it to afflict pain on other creatures. The evil actions of one animal may affect many, such as a bobcat killing a mother duck may lead to the death of her newborn ducklings. Satan influences human beings to commit evil acts and afflict pain on others, thus Satan may have also corrupted the animal creation.