I personally have never met one I really thought they deep down inside believed there really was not a God. They remind me of children throwing temper fits against mommy, "I hate you Mommy".
I feel the same way about the Tooth Fairy and Santa Claus. None of these entities have been seen (at least in the past 2000 years) and none have done anything to prove they exist-- like performing the impossible (not just merely the improbable).
There isn't even any verifiable value to strongly believing God. Matthew 21:21, John 14:14, Matthew 7:7, Matthew 17:20, and Mark 11:24 didn't ring very true for Jessica Lunsford in this life, regardless of what castle in the clouds she gets in the afterlife.
Belief in God is just another anti-depressant, like Paxil, Prozac, or Zoloft. People are scared that there isn't some magical place to go to when they die and they are scared that there isn't a magical invisible man who can rescue them like a safety net when they need rescuing.
I think it's generally as harmless as people taking anti-depressants in pill form. It helps people to function when they would have difficulty doing so. Whatever. It doesn't really affect me.