|the nerve-eater of Zur-en-Aarh|
I am utterly fascinated by the question "What evolutionary purpose does a belief in free will serve?" Nearly all Human cultures evolved to believe in free will, so it would seem superior. I think the ability to blame people for their "choices" must come into it. Someone who commits an anti-social act (murder or whatever) is more likely to do it again, so the ability to blame them soothes us for punishing them (more murder) and soothes us that we wouldn't do the same.
I do not think that is actually necessary, though. Creating strong disincentives for murder or other heinous acts, in order that a rational human will deterministically react to by not committing murder or whatever, does not require free will in any part of the equation.
Also, I would query "nearly all human cultures evolved to believe in free will", or at least to the extent free will works in Golarion and in the versions of D&D preceding Pathfinder, which is ultimately coming from one specific thread of early Christianity. Just out of the bits of history and culture I am reasonably familiar with, I can cite Norse wyrd, Classical Greek moira, geasa in the original Irish mythology, and the more predestination-oriented strands of Christian thought as counterexamples, and all of the more restrictive.