Atheists are good people only by relativistic standards that they have created to suit themselves for whatever moment is appropriate for them. There are no moral absolutes with atheism. With no absolute objective standards of morality, then whoever is in power of a given relationship gets to set the standards, and this opens the door to unspeakable cruelty. In fact, the great appeal of atheism is that it so conveniently provides every reason someone could imagine in order to be immoral. Without any objective absolute standard of morality, you are really unable to condemn any choice regarding morality whatsoever. And thus, the great appeal to atheism is also its obvious undoing.
You imply that atheists are noble people because "their morality stems not from a fear of punishment, but a simple belief in treating others well". This is hogwash!. The morality of the atheist is simply self-centeredness and self-deception (deceiving others is also appropriate in this system).
I suspect that your statement was also intended to be a swipe at Christians since you probably mistakenly think that their morality stems from "fear of punishment". On the contrary, a Christian is someone who is no longer under God's righteous condemnation of his sins (see Romans 8:1) because of the person and work of Jesus Christ in his behalf. As a result, Christian ethics is based on the right standard (God's objective written Word), flows from the right motives (gratitude and love to God, and love to our fellow men who are created in his image), and is aimed at the right goal (the glory of God).