The question asked of me was, why atheists say that there is no god.
I do not dismiss god out right, I give the existence of any type of god a 0.01% chance. This comes from everything that I have studied over the years. For me it all started when I was a hardcore xian and I set out to prove to all the naysayers that the bible was correct. I read it, the bible, and found all kinds of contradictions, so I began looking for physical evidence to support the bible. What I found was far and few between, and it did not support the bible enough to make it conclusive.
Then I began to look at all the other religions in the world, both ancient and modern. Then I began to put it all on a timeline to see how it all fits together. The xian religion is a very young religion which appears to be a copy of other older religions.
Religion is an invention of man to try and explain that which man does not understand. Some people need religion in their lives because they have not evolved beyond the need for a "sky daddy" to help guide them through life. Many of us have grown up and moved beyond the need for such imaginary friends.