It is simply meant to illustrate a point: If our hearts tell us there is evil in the world—that certain acts are horribly wrong because they transgress our dignity and worth—then retreating to atheism doesn’t help us, since atheism—to be consistent—can’t provide a basis for human dignity in the first place. In this regard, evil is just as much a problem for the atheist as it is for the believer.
Dr. Jay Sklar (Assoc. Prof. of Old Testament at Covenant Theological Seminary) has written an excellent article for ByFaith Magazine on the subject "Why Does God Permit Evil?" Here's the link. I commend it both for those who struggle with this questions as well as for believers for edification and a resource when called upon to provide an answer to this question.