Most ideas of right and wrong, reward and punishment, acceptance and rejection in many societies have a basis in the religious culture.
This being so, why would an atheist believe in morality? If there is no accountability, why should anyone be "good" or "bad"?
An animal does what it can to survive; there is no "murder" or "theft" or "rape" or "infanticide".
So why should there be ANY standard of behaviour for humans?
No trolling please; I would really like to discuss the topic (Jimmy, this is for you) from an atheists point of view.
Some morality are based on social constructs and some are measurable and tangible. That is, they are consistent throughout human evolution.