Let me start of by saying that I don’t believe all atheists are amoral, its just that the athiestic worldview taken to its logical conclusion cannot offer a basis of morality. In other words theres no space for absolute for Absolute Objective Morality. Let me explain:
Morality can be Subjective or Objective. Subjective Morality differs from person to person. What one determines or “feels” to be right. That creates a problem. What I say is wrong, someone might say is right. I might say stealing is wrong. But the person who’s stealing from me might say that he’s stealing to feed his family so theres nothing wrong since its for a good cause and from his perspective, no one is getting hurt by his theft. Now if we were to say stealing is wrong matter what, that begs the question “according to whom?”.
So if we were to say that there are certain absolute objective moral rules, that don’t change no matter what, that exist outside of us, then we have to assume and external lawgiver, which according to atheism cannot exist.
That is the fundamental failure the atheistic worldview. It simply cannot account for or explain morality.
Atheism, as a worldview is morally bankrupt and cannot fully explain the various questions such as morality, existence and meaning that a coherent worldview must answer.
So atheism fully embraced cannot talk about good and evil, because according to its perspective there is not absolute “Good” and “Evil”. When atheists pose the existence of evil and conundrum to disprove the existence of God, it seems that the existence of God is necessary to provide the moral framework for the atheist to define “Good” and “Evil”.