Is credulity adaptive?

This past Tuesday, while my boss and I were driving out to the sort centre, there was a feature on The Current about a self-help film called The Secret. It's really a rehash of old ideas like "the power of positive thinking" (as touted by the "deep philosopher" Norman Vincent Peale). My boss likes most of the proponents quoted on the show. One thing that he mentioned in passing is the fact that most of the proponents of this sort of thing are quite religious (as he is) while most of the critics are atheists or agnostics (like yours truly). This seems to be true (Peale, for instance, was a preacher) and it got me to thinking about why this might be. There's nothing obviously wrong with the idea of positive thinking, though I agree with the critics that, pushed too far, this could lead to a blame-the-victim mentality (Lost your job? Got mugged? Raped? You must not have been thinking positively enough!). The thing is, though, if you're an atheist or an agnostic, your beliefs are going to depend on such annoying little things like evidence- and if so, you're likely to have a hard time thinking positively about yourself unless you're already doing well. I know that I do.

Given this, it's not too big a stretch to suggest that a certain amount of credulity might be adaptive. Not too much, obviously (otherwise everyone would take advantage of you) but some. This might go some distance towards explaining why so many people fall for shit like this, this, and this.