In Frank Turek's latest article, Sleeping with your Girlfriend, he explores some of the reasons why atheists willingly choose to reject God.
"I’ve found that the machine-gun-objection approach is common among many skeptics and liberals. They throw objection after objection at believers and conservatives but never pause long enough to listen to the answers. It doesn’t matter that you’ve just answered their question with an undeniable fact—they’ve already left that topic and are rattling off another objection on another topic as if you hadn’t said a word. They don’t really seem interested in finding answers but in finding reasons to make themselves feel better about what they want to believe.
After all, a skeptic of one set of beliefs is actually a true believer in another set of beliefs...unbelief is more motivated by the heart than the head." 
Check out the entire article here.
Courage and Godspeed,
Chad A. Gross
1) Dr. Frank Turek, Sleeping with your Girlfriend, http://www.crossexamined.org/blog/?p=98, March 2, 2009, Emphasis mine.