"Frank is a Christian who believes in God and follows the morals and
ethics taught by his religion. Doug is an atheist who does not believe
in Frank's God. Therefore, Doug does not have morals and ethics."
This is exactly equal to:
"A dog is an animal. A cat is not a dog. Therefore, a cat is not an
Whether the cat is a dog or not, does not mean it is not an animal.
Just so, just because a person does not believe in God, does not mean
that he does not have morals and ethics. There is no argument that can
prove that morals and ethics originate in any god.
Morals and ethics are a product of the society in which one lives. If
that society is strongly influenced by a particular religion, that
religion's beliefs will be echoed to some extent in the ethics upheld by
that society, particularly in its system of laws. One can of course
overcome one's societal influences.