If everything has a purpose then evil doesn't exist

[Mister Agenda]

I'm not dismissing their potential psychological value, but there's no convincing evidence that the visions originate from anywhere but inside our own brains.

If the purpose of a successful vision quest is to gain access to knowledge not previously known, then how can you claim the vision was a product of our own brains? How can a brain produce knowledge that it does not correctly possess?

Because it having a purpose of gaining access to knowledge not previously known doesn't mean it can actually give you knowledge not previously known. If you think visions give you knowledge that you don't already know, that's testable. We know how to induce visions and we know how to make information inaccessible to someone. Have at. Until a vision can produce inaccessible knowledge under controlled conditions, the conclusion that they are hallucinations under stress is the most parsimonious. Sometimes those hallucinations can provide insight that would otherwise be locked in your subconscious; or inspire you to change your ways, and that's nice.