Depends of what you mean by God (no pun intended) I by God one means everything or the universe as pantheists or so called deists do, Then we can't possibly know. If that's what people mean by God, Then it is an irrefutable claim to say that it exists. One must logically be agnostic to that proposition, And must say he doesn't believe because no proof has convinced him. But that of course is not what most people mean when they say they believe God exists. For if by God one speaks of an omnipresent, Omniscient, Omnibenevolent, Omni temporal being that possesses consciousness, As major religions like Christianity and Islam believe, Then one can say he is gnostic about the claim and must logically say he doesn't believe, Not only because their is no evidence to support the claim, But also because there is proof to the contrary. The problem of evil is the obvious rebuttal, But the problem of free will is another. To keep things simpler and not talk past one another, We should clearly define what we mean by God and then define our position.