Point: Atheists cannot be moral.
Morality must be derived from a higher authority than the actor. Without a higher authority--God--from which to derive a code of morality, then each person must define a "moral code" for themselves. This reduces "morality" to essentially acting according to what is one's own nature, anyway. If morality is simply acting according to one's own nature, then no one could be anything except moral, and morality becomes meaningless.
This is not to say that atheists cannot behave in ways that society considers "good," only that they cannot be defined as "moral" people.