To all who believe there is a God, let me ask you a simple question:
Do you believe in unicorns? Do you believe in Santa Claus, the Easter Bunny or the Tooth Fairy? Do you believe there is a tiny teapot orbiting the earth as we speak?
I'm assuming that most people on this forum have an IQ higher than their last test score, so I'm also going to assume that the answer to all of these questions is no. How do we know that none of these propositions are true, though? There is no conclusive way of proving that unicorns do not exist, because there is always the possibility that they might one day be discovered in the forests of Borneo. Because of this, we all have to be agnostics when it comes to unicorns, strictly speaking. This does not mean, however, that the average, reasonable person believes that the probability of unicorns existing is exactly the same as the probability of their not existing. Most people live their lives as though unicorns did not exist, and then wait to be proven wrong.
This principle is applicable to God. As things currently stand, there is no empirical reason for believing that there might be a creator deity up there somewhere, influencing our daily lives. This is not to say that God does not exist. One day, the Hubble Telescope just may take a photograph of God, floating around in the intermundia. If that happened then I, as an atheist, would be prepared to change my position. So, I suppose I would technically be described as an agnostic. However, because I am also a rational, reasonable person, I choose not to believe in anything for which there is no evidence. There is no evidence for God, and until anyone proves otherwise, I see no reason for believing in Him.
The atheist v. theist argument should be as simple as that.