Brief thoughts, triggered by a discussion. The other person is Christian, hence I neglected to generalize my comparison to all religions, but that's not important. What is important is that the concept of atheism is poorly understood. In discussions of atheism, a commonly seen refrain is, "Atheism is simply the lack of belief in a God." While basically true, this definition is shallow and open to misconceptions. By expanding a little on the concept of atheism, I hope to reduce its ambiguity, and shed some insight on what it means to be an atheist.
What are the consequences of disbelief? Well, to examine that, I need to present a comparison with the consequences of belief. There is something extremely comforting about belief in God, and that is the idea that humanity's existence has a meaning preordained by God. We are special, because God made us, because God says we are special, because God cares about us. And with that comfort comes the responsibility to obey the laws God laid down in time immemorial, because that is how humanity is expected to express its meaning. I won't get into arguments about inherent sin and how that affects the meaning of humanity and so on, because that is an extremely deep topic, and not central to what I'm trying to say anyway.
So that's the basic scenario from a believer's viewpoint. What happens when we take the belief in God away? First, we remove life's preordained meaning. Some people just stop there, and wallow in the apparent meaninglessness of life without God. Christians mock them, and deservedly so. But I want to talk about atheism, not nihilism, so let's look at the rest.
Lacking belief in any divinely inspired meaning to life, and unwilling to believe that there is no meaning to life, these people are left to determine the meaning of life for themselves. Another target for Christian mockery--they think people choose atheism simply to get away from the strictures and morals of faith, and do whatever they want under the guise of relativist morality. Maybe some do. But that is a child's conception of freedom. With the freedom of self-determination comes the responsibility to seek a productive, beneficial, and meaningful philosophy of life, and to live up to that philosophy as best one can. In my view, it is this essential recognition--that the right to think independently carries the obligation to think carefully--that makes atheism a viable, positive way of life rather than a mere denial of religion.