I wonder to what extent the insanity potential of spiritual endeavor is precisely the reason so many hold tight to prim and proper rules and definitions and text-based support mechanisms.
And I wonder as well to what extent those who are crazy use spiritual endeavor as a means of excusing their insanity and never consent to do the work that might straighten things out.
I haven't got the energy to cite chapter and verse and support my assertions, but I have seen such things (and certainly indulged them) and am interested in their potential to throw the spiritual aspirant off course and into the maw of self-serving confusion, be it super-sane or insane.
I once went to a private meeting (dokusan/sanzen) with a Zen teacher who had previously given me a koan to work on. I had tried on several occasions to give some satisfactory answer to the question posed and each time had come away rebuffed. So on this particular occasion, I reached back into my knowledge that came from reading and thinking and feeling and gave an enormous shout.
The teacher looked at me mildly and then said, "You know, you don't have to be crazy in order to do this stuff."
The way I see it today, if there is something special or separate or improved about spiritual practice and its outcomes, this is a definite hint that you are off your rocker.
A rich understanding is richer than that.