For people who are raised with religion, it's hard to imagine morality without a god.
As a child I was told that God had a giant book with the names of every human being on Earth, and that he put a check next to your name every time you did something bad. Of course, since God is everywhere, even in your mind, you could get a check next to your name just for thinking something bad. When you die, I was told, God adds up all your check marks from your entire life and decides whether you go to Heaven or Hell.
This wasn't something I learned officially in Church, but for some reason, this was the version of God's judgment that made the most profound impact on me, probably because I'm a very visual person. Every time I even thought about doing something bad, I had a vision of God opening up that massive book and turning to the page with my name. This vision did a good job of keeping me from many little childhood sins like lying, stealing candy and what not (that's not to say that it worked perfectly).
But that's not morality. Refraining from doing bad things because you think someone can see what you're doing isn't the same as refraining from doing bad things because you're a good person.
As for bigger sins, like hurting others, I never had a desire to hurt anyone. When I hurt someone accidentally, I felt genuinely sorry for the hurt I caused that person. Fear of a god had nothing to do with it. So when people say things like, "Well, if you don't believe in God, then you can just rape and murder because there are no consequences," they are saying that their fear of a god is the only thing that keeps them from raping and murdering, and while that statement may be true for them, I don't think it applies to the majority of people.
The fact is that morality is hard-wired. On the broader points like rape, murder, or theft, we all know right from wrong. On the finer points like marriage or prostitution, opinions vary from person to person and culture to culture. How far an individual deviates from their own or their culture's accepted standards of behavior has nothing to do with any supernatural beings in the sky. Individuals, and sometimes entire communities, will either find a way to justify doing something they know is wrong, or they will feel guilty for doing it, but do it anyway. For people who are mentally ill, people whose hardwiring has short-circuited, no supernatural being can convince them to behave morally, even with the threat of eternal damnation. The BTK killer, for instance, was a pillar of Christ Lutheran Church in Wichita, Kansas, as well as one of the most horrific serial killers in American history.
If gods and religion have no impact on a person's morality, and atheists are just as moral or immoral as anyone else, then how can I say that Atheism is superior to a supernatural belief system?
The aspect of Atheism that is superior to religion is that it is rooted in logic and reason.
Children raised with religion are told not to do bad things because their parents say so; because the preacher says so; because God says so! Faith in authority figures is valued over rational thought. As a result, many children are not given the opportunity to develop their rational mind. They are trained to be motivated primarily by their fear of the wrath of authority figures.
My children are told why something is right or wrong. They shouldn't steal because they're hurting the person from which they steal. They shouldn't lie to their parents because their parents have more experience with the world and wish to guide them through the rough spots; every punishment is done with love and for their benefit, so they must be honest about what they've done and accept the consequences because they will be stronger for the experience. They mustn't lie because lying is weakness. They mustn't lie because there will come a time in their life when all they have is their word, and if they don't have their word, they will have nothing at all.
It is profoundly more difficult to explain the logic behind the values you are trying to instill in your children than to say, "Because God says so," but instilling rational thought as well as morality in a child is immensely more beneficial to them.
In the end, my kids will probably lie or steal as much as the children of the Christians next door, but what my children will not do is believe what they are told without rational explanations. They will not be led into a war on flimsy justifications. They will not follow authority figures simply because they are afraid to question them. They will not be capable of blind faith. They will not shut-up and get in line.
They will be strong-willed and capable of leading others, not as shepherds of mindless sheep, but as leaders of intelligent human beings.