Really? Isn't the mind of the observer of "spiritual revelation" as limited as any other human mind? Consider Joseph Smith, Mohammed, Baha'ullah, at al; "there will be many false prophets"
I am not at all sure which (if any) of these prophets was a conscious fraud; my own take is that most of them had some sort of epilepsy or schizophrenia. I am fairly sure, however, that not all of them were receiving prophecies.
If one accepts the hypothesis that there are spiritual beings, it's possible some of them were actually channeling demons or devils or some such. But there is really no way to know.
"Look at the fruits". Does this make Mormonism true?! It's fruits look pretty good to me.
A friend of mine "hears" the Virgin Mary, except when he's on anti-psychotic medication. I take the fact that the thorazine stops the voices as evidence thy're not really the BVM's.
If something like "spiritual revelation" ever happened to me, I'd make an appointment with a neurologist to see if I had epilepsy or a brain tumor or such like.
The problem with your (one-sided) characterization is that you can't build a civilization from thorazine and epileptics.
UNLESS it was a real one.. then;
You might blow the neurologists mind.. on that visit.. IF he were lucky..
Andrea Yeats vs Joan of Arc: both had "more certain than any other type of knowledge" it seems. Of course, Joan was responsible for far more deaths.
When I said Spiritual revelation is the most certain knowledge, I was speaking of Christian Spiritual revelation. In such revelations, there is no "observer".
The first Spiritual revelation a Christian receives is that "Jesus Christ is Lord". It doesn't come from his own mind, rather the Truth appears in him. But because of the revelation, we believe, He "knows" us and we are born again by and in the Spirit.
We are no longer "observers" - we abide in Him and He in abides in us. (Gospel of John, etc.)