The Problem of Evil is a pretty difficult one for Christians and other theists. One response to it is to say that atheists have a problem too, either because they also must cope in a world with so much evil and suffering in it, or because without a way to “ground” morality, they have no basis to call anything evil. As we’ll see, these are both Bad Arguments.
Bad argument: Atheists must cope psychologically with evil, and this is a problem for them
Stephen Law dealt with the response that atheists must also cope with the evil and suffering in the world (which actually came from an agnostic, not a theist, in the linked example). As Law says, this sort of response relies on shifting the problem we’re talking about to the problem of how to cope psychologically with evil and suffering (which is indeed a problem for both theists and atheists). But this is not the problem that the discussion was originally about, which is that evil and suffering make theism less likely to be true (i.e. they’re evidence against it), but are not evidence against atheism.
Bad argument: Atheists have no grounds to call anything evil and so cannot make an argument from evil
Wintery Knight and Cornelius Hunter are both Christians, and both make the second sort of argument: if there is no God, they say, there is no matter of fact about what is evil, it’s an entirely subjective judgement either of particular individuals or of human societies, and as such cannot be binding on God.
Firstly, both Knight and Hunter just assert that if there is no God, there are no moral facts1. But in fact the philosophical debate about whether there are moral facts is carried on largely without reference to God: there are atheists who say there are, and atheists who say there aren’t, and a lot of debate about just what it means for something to be an objective moral fact anyway. Apologists like to pick an atheist who says there aren’t moral facts and quote them as defining The Atheist View on Moral Facts, as if there were only one.
But suppose for the sake of argument that Knight and Hunter are right, and if there is no God, there are no moral facts. Conventional Christianity still faces a problem of evil as an internal contradiction. Here’s a little argument from evil:
1. If God exists, God is objectively morally perfect.
2. If God exists, it is objectively morally imperfect for someone to permit human suffering which it is in their power to alleviate (see the Parable of the Good Samaritan, for example).
3. There is human suffering which it would be in God’s power to alleviate, were God to exist.
Now, assume for the sake of argument that God exists. From 3, suffering which it is in God’s power to alleviate exists. From 2, God is objectively morally imperfect, but this contradicts what we get from 1. So God does not exist, proof by contradiction.
Any theist worth their salt will attack premise 2 (and probably say that there should be a “without good reason” after the “permit”, and then say that God either has good reasons or that we have no way of knowing that he doesn’t). But my purpose isn’t to present a comprehensive argument from evil, but rather, to point out the shape of the argument: notice that the argument does not rely on a claim that there are in fact objective moral values, only that if God exists, there are, something which Knight and Hunter agree with. In fact, more robust arguments from evil generally rely on putting together statements which theists should accept and showing that they lead to the conclusion that there is no God.
A couple of Knight’s commenters (1, 2) point this out to him (one even explicitly telling him that the Argument from Evil is what’s known as a reductio ad absurdem) but he just doesn’t seem to get it. I hope you do, but let me know if this could be clearer.