Is God a conspiracy theory?

The psychological explanations for religiosity also apply to conspiracy theories. They are two aspects of the same thing, and they are a natural part of human nature. 

Technically, it's a cognitive bias known as “fundamental attribution error” - the tendency to overestimate events as being intentional rather than the product of random situational circumstances. 

This bias exists in our minds because it provided us with an evolutionary advantage - it enables us to make sense of the world by providing simple explanations for complex events - giving us the sense that we can be in control and enabling us to avoid "inconvenient truths"

Here's a summary:

Both religion and grand conspiracies are immune from reason and both are impervious to evidentiary standards.

Both religion and grand conspiracies ascribe great power to "invisible" forces.

These "invisible" forces appear to be as omnipotent as are Gods in the various religious traditions.

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And here's a good article giving an overview of recent studies...