I agree with Octathlon - from the Buddhist perspective, the danger in belief in an eternal, omnipotent creator god is that it is in direct contradiction to the three marks of anatta, annicca and dukkha.
But if I may speak outside of the Buddhist perspective: the danger of this type of belief can be in the fact that if one believes that this god has absolute power over the universe, and knows everything everyone does, then there isn't much room for free will, which makes any attempt to "change" as a person futile. Furthermore, if this god claims to justify the punishment of nonbelievers, then the person who believes in this god will find all manner of mental justifications to do harm to others in the name of this god.
In any case, there is a danger in believing that you are absolutely right in what you believe and everyone else is absolutely wrong. I know many "god-fearing Christians" who are quite tolerant of other beliefs and don't necessarily claim to be following the only true religion. However, I do believe that, based on experience and history, belief in the commonly worshipped Judeo-Christian god is dangerous because the texts attributed to this god is chock full of horrendous acts against humanity justified by religion. One can choose to ignore the bad parts of the texts, but then there is a sort of cognitive dissonance created, especially when pressed by others to give a good reason why they are still Christian even though they are rejecting a large portion of the "holy" text.
I think belief in a god predisposes one to fanaticism and intolerance because you're relying on an outside source as the definitive and final word on all aspects of life, instead of investigating for yourself these things to see if they are actually true or relevant to your everyday lived experience. This outside source can tell you anything and everything and you'll believe it because you've already convinced yourself that this outside source is the final word.
The last thing I'll say is that, in my experience, fundamentalist Christians believe that any wholesome action a "non-believer" does is incapable of producing the same so-called positive benefits of the Christian because it's not based in Christian behaviorism. So even if a person is the nicest, most caring, most giving, most compassionate person you can ever meet, they will still meet with a terrible afterlife simply because they don't believe in god. Monotheism predisposes one towards a monopoly on morality, which is often used as further justification for persecution of others.