This is an epistemological postulate that our knowledge must be grounded in some fixed point, "unmoved mover" if you will. I have no problems with epistemological postulates who share the same ontological status with tooth fairies and literary characters - they are products of the human thought process. I do have a problem, however, when epistemology is mixed up with ontology, and a product of human thought process becomes an objectively existing super-entity. It is like trying to attach a real chain to a link painted on a wall.
However, most god-fearing folk are too narrow minded to understand the relationship between epistemology and ontology. For them, god is a feel-good concept that has no specific meaning but evokes childhood memories of safety and security provided by parental authority figures. The yearning for that safety and security is what prompts insecure minds to invent gods. The connection between the concepts of deity and childhood experiences of parental authority figures is so friggin' obvious that people tend to take it for granted and altogether miss.
Wojtek