Some atheists act like they "know" similar to how theist act like they "know". Some Atheists try to defend atheism with "occam's razor" but the principle of Occam's Razor recommends selecting the competing hypothesis that makes the fewest new assumptions which means the principle of Occam's razor is against both theism and atheism and therefore is for agnosticism. Atheism can never be rooted in science. The scientific attitude favors agnosticism. In science you don't know what you don't know. If atheism meant "not believing in god" then atheism would be scientific and the same as agnosticism but if atheism means "believing that their is no god" then atheism becomes unscientific. The type of atheist that is not asserting the belief that god does not exist is barely distinguishable from the agnostic who does not incorporate god into their theories. This difference become a question of semantics. But the more assertive atheists who believe that there is no god are more like theists than they are like agnostics because these atheists choose to believe something for which they have no evidence.