Arguably the most famous argument for atheism is the Problem of Evil, most notably formalized by David Hume. There are different versions of the argument, but all of them purport to show a contradiction or at least a very strong tension between two propositions that most theists believe: 1. God exists as an omniscient, omnipotent, perfectly benevolent being and 2. Evil exists. There are several popular objections to this line of argument, but one argument is particularly confused.
The objection is that without God, there is no objective morality and therefore on atheism, the Problem of Evil could not get off the ground, precisely because a key premise (Evil exists), presupposes theism. I've heard this objection from pre-suppossitional apologists, but also from famous apologists like Ravi Zacharius and William Lane Craig (though to be fair to Craig this was not his main objection). This objection fails, however, because the proposition "Evil exists" is not necessarily a premise of the Problem of Evil.
Let's concede the controversial premise "If there is no God, there is no objective morality" or better yet "God is a necessary and sufficient condition for objective morality". The Problem of Evil can obviously still be ran. One way is as follows 1. If God exists,(and only if God exists), then killing, stealing, rape, ext. are evils acts. (Based on conceded premise that God is necessary for objective morality). 2. If God exists, then God would prevent evil acts from existing. ( Based on the contradiction between God's goodness/power and the concept of evil) 3. Acts of killing, stealing, and raping exist 4. Therefore, there is no God.
The argument is valid, and if all the premises are true, then the argument is sound. This shows that an argument from evil can be used to refute theism, even if it is conceded that theism is a presupposition of (objective) evil. Of course, if the above argument is sound, it would also follow that there is no objective morality. The argument can thus be ran by someone who doesn't even believe in objective evil, like John Leslie Mackie. For someone who does believe in objective morality and that premise two is sound, premise one would have to be denied. Most theists, however, would not like to give up God's necessity for morality, and thus would want to deny premise 2.
When faced with a variation of the Problem of Evil, therefore, theists should focus their efforts on denying the premise that contends that God would not permit or will evil to exist. As long as such a premise is sound, the Problem of Evil would still be alive, no matter what God's necessity is for objective morality.
