From here (breaks added):
We’re atheists because, every time in history that we’ve come to a better understanding about the world, that understanding has always been one of physical cause and effect.
We’re atheists because claims from the past about miracles and so on have always come from unreliable sources, and have never once been substantiated.
We’re atheists because, over the decades and centuries and millennia, religions have risen and fallen, not because they’ve been better supported with good evidence, but for social and psychological and political reasons, entirely consistent with them being entirely made up.
We’re atheists because religion has had millennia to prove itself right — millennia in which it has dominated the intellectual and scientific discourse, for all but the past few decades — and has utterly failed.
We’re atheists because the religion hypothesis has been tested — and tested and tested and tested, and tested again, and tested yet again, and then tested one more time to be sure, and given the benefit of the doubt and tested again, and then again, and again — and has never, ever, ever panned out.
— on why atheism won’t be proven wrong the way arguments against it work today.