Criticism of faith
Such arguments are largely grounded in an "empiricist" worldview that is purportedly based on the scientific method, in which the truth of a proposition is decided based solely upon the observable evidence for its truth or falsity. In this worldview, a lack of conclusive evidence means that a proposition is just as likely to be false as true, and therefore should not be believed to be true.
Hence, within this worldview, faith (of the sort described in Hebrews 11:1) is seen as "irrational" or unacceptable, in that it involves believing in the truth of some proposition even if there is not evidence enough to satisfy the empiricist. The well-known atheist Christopher Hitchens, in a particular criticism of faith in miraculous healing, said, "What can be asserted without evidence can also be dismissed without evidence."
With particular application to faith in God, atheists will often argue that they do not believe in God, or that God should not be believed in at all, due to the lack of evidence for his existence. Theists have responded to these claims by stating that such evidence does exist, but that atheists reject it out of hand.