The fact that many people are just naturally atheist because of God's 'hiddenness' without necessarily opposing theism is itself a strong argument for atheism. Philosopher John Schellenberg developed this argument and wrote a book about it, and you can read an article by him on infidels.org.
What Divine Hiddenness Reveals, or How Weak Theistic Evidence is Strong Atheistic Proof (2008)
http://www.infidels.org/library/modern/john_schellenberg/hidden.html
Likewise, the philosopher Theodore Drange has developed a similar argument, called the Argument from Nonbelief (ANB), also on Infidels.org at the link below:
The Arguments From Evil and Nonbelief
Theodore Drange
http://www.infidels.org/library/modern/theodore_drange/aeanb.html