The fool says in his heart, 'There is no God.' – Psalm 53:1
In his book On Guard, Christian apologist William Lane Craig makes the point that traditional atheism has pretty well disappeared. Having been confronted on many levels by able defenders of the Christian faith, philosophical atheists have concluded that it is impossible to prove a universal negative (such as "There is no God."). As mankind's knowledge of the universe is not exhaustive, one can no more say "There is no God" than one might say "There are no 12-legged cyclops." Just because we have never seen a 12-legged cyclops hardly means that in the vastness of the universe there might not be a 12-legged cyclops. In the same way modern atheism is willing to assert that there MAY BE a God or god somewhere in this vast universe. But having not seen that God the modern atheist has now redefined atheism NOT in terms of there being no God/god, but as an unbelief in any God/god. Dr. Craig points out that given this new definition of atheism (which I have above called apisteuism, meaning, no belief), then babies are born atheists, and all our dogs are atheists, as none of these "believe" in God.
This is a tricky business: the changing of the meaning of words. Indeed, the case could be made that these modern "atheists" have abandoned atheism for apisteuism. The irony of this is that Jesus identified this unbelief as being at the heart of men's problems long ago. For in John 3, after stating that "whoever does not believe (in him, meaning Christ) is condemned already" (3:18), he went on to say, "The light has come into the world, and people loved the darkness rather than the light because their works were evil" (3:19). That is, they didn't believe because there was an issue of deep-seated guilt behind their decision to not believe. People were, and are, afraid of having their (evil) works exposed (John 3:20). This modern redefining of atheism as actually being apisteuism – an unbelief in the God of the Bible – fits with what Jesus saw as the real problem and lays things out as they really are.
So "hurrah" for the Christian apologists who have argued well their case, and "hurrah" for the (formerly self-defined) atheists who are now willing to state their issue for what it really is: a refusal to believe.