To satisfy material needs and primitive instincts. Right and wrong is a human construct. As such it can be anything humans deem it to be.Most atheists if not all atheists I know believe in good and evil, in morality, in there being value in helping each other, doing good for others. Many are generous people who help others when it's hard and even miserable for them and do it out of the kindness of their heart. It's important to do the right thing during this limited time we're here in this world, it's all that really matters. But I'm sorry, that really has naught all to do with belief in a God, for any of us.