For an atheist to be an intellectual thinker, they must admit to being agnostic as you can not prove that God doesn't exist. Not in less, you are all-knowing, outside of space and time, infinite, and all-powerful could you even possibly get the chance to say there is no God, and that would take that individual having the status of God to do so which is impossible.
So even though you can not prove God doesn't exist even if He was completely absent like a deistic God (no evidence on Earth still doesn't prove that God isn't outside of space and time) we in counter have a God who has great evidence for his existence.