This article “The return of the village atheist” addresses the problems with atheist fundamentalism and religious fundamentalism. I agree both types of fundamentalism share the same element of asserting certainty in their own ideology while not accepting any other ideology as true.
On one hand, atheist fundamentalism may have a healthy scepticism and doubt against the claims of religion, especially those that attempt to control people with guilt and fear, but it tends to close its mind on the possibilities of supernatural or metaphysical workings in the universe (which may be observed by quantum physics), such as telepathy and energetic healing. On the other hand, religious fundamentalism tends to interpret scripture literally and close its mind on scientific reasoning and archaeological proofs that debunk myths and dispel superstitions.
So, perhaps the middle path to avoid both types of fundamentalism is to stay in a state of awareness and wonder and keep an open mind to possibilities. It can be a healthy combination of doubt and faith, or scepticism and hope, for a mystic can be both an agnostic and a gnostic – admitting one does not know everything about God for certain, but at the same time, acknowledging one has an intuitive knowing about the Divine that cannot be explained fully but can only be appreciated for what it is – a mystery.