I'm no religious expert, certainly, but I'm fairly certain God gave us free will*. Which of course includes believing whatever it is we want to believe.
Also, the whole getting into heaven vs. eternal condemnation thing comes down to repentence. As in, after dying, you come face to face with God, and say "oh snaps, oh do exist, my bad!", and are allowed into heaven, regardless of your athestic life you lived on earth.
*assuming you believe in of all that.