Really? Show me an atheist who "knows." I've never met one in spite of years mixing in atheistic circles. Tosh!

Richard Dawkins. Now there's a man who doesn't "not know".

Our Steve Shaw has demonstrated the arrogance of ignorance. The bubble mentality. I ain't seen it, it works here. Therefore there is no other viewpoint.
Fundamentalist Religions also demonstrate a similar arrogance of the only view worth considering.

My original assertion that "Atheists know" is that most atheists I know prefer to know, and if that is not possible they are content to know that KNOWING it is an assumption, a theory that is yet to be proven, a work in progress, but the one they prefer. Though some exceptionally intelligent exceptions occur. And publish books on the subject.