From a purely rational point of view belief in God is farcial for arguments i have outlined (ie. lack of evidence).
Independently God seems at odds with the findings of modern science: Deterministic laws govern everything observeable in the universe, if there was a God we would expect to see his presence in the findings of science: We do not.
Independently the "God model" is internally inconsistent: an omniscient, omnipotent, benevolent God is starkly at odds with the vengefull, egotistical, inferiority complex God presented in the bible.
It is also extremely externally inconsistent: The perfect God would produce the perfect creation; a perfect craftsman produces the perfect craft....... the world is certainly not perfect. Why for example (and i can give many many more) is it that the digger wasp and its cousin Ichneumonidae reproduce by paralysing a catapiller then laying its eggs into its body only for them to hatch and then eat there way out of their helpless host?
(Ichneumonidae lead Darwin to lose his faith for precisely this reason "I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars")
From a psychological/anthropological view we can rationalise very well why religion and religious views exist. In addition and supporting this we can see that the correlation between religious beliefs and religious upbringing is so strong that religion to all extenses and purposes can be viewed as a cultural phenomenon.