Most of the people who believe in God are doing blind belief, the majority of the people in the world are blindly following the religion of their fathers. An atheist, on the other hand, even though he may belong to a religious family, uses his intellect to deny the existence of God; what ever concept or qualities of God he may have learnt in his religion may not seem to be logical to him.
For an atheist to say ‘there is no God’, he should at least know the concept of God. His concept of God would be derived from the surroundings in which he lives. The god that a large number of people worship has got human qualities - therefore he does not believe in such a god. Similarly most people too does not and should not believe in such false gods.