As an atheist, I am saying "I don't know if there is a God". That is quite different than saying "There is no God." However, Geoff is saying "There is a God". If he said "I don't know but I prefer to believe there is a God" then I doubt there would be so much controversy in here.

Part of the problem is that when atheists say "There is no God", they really mean "Although it is possible that God exists, there is not currently convincing evidence of God". To atheists, it is no different than saying "There is no a Yeti in Tibet who can play the piano". It is possible that such a Yeti exists but since there is no evidence, most people take the stance that they will believe it when they see it. Unfortunately it is much shorter to simply say "There is no God" and that causes a lot of misunderstanding.