I was an atheist for a long time. I never could see how one could construct a coherent morality. Without a god, we are all just bits of matter assembled in a particular way. Smashing the competitions skull is no different that two space rocks colliding. The concepts of right and wrong are devoid of meaning.

Every argument for a godless morality I have seen essentially boils down to "well, it would suck to live in a world where everybody acted like _that_," (so what?), which I even less compelling than "don't do _that_ because god said so."