I was about to post a followup comment to James' case against the spirit world post, when I realized that I could get more people to read it by actually using the awesome influence granted me as an editor.
I think a kind of agnosticism is the only sane way of dealing with these things. One need only ask James Kent what kind of scientifically final proof he might expect to be able to offer which would finally, objectively and incontrovertibly convince every explorer, shaman, tripper, guru, lama, priest, and new-age party kid that his theory is "more real" then their own personal experience.
The very idea is contradictory: a person who believes someone else's theory over their own experience is not rendered more sane, more in touch with reality, merely because the theory in question happens to be James Kent's.
Clearly there are countless people who have had spiritual experiences through various means, which they experience as valid. The Catholic Church, as an institution spanning back almost 2000 years, has refined the art of using devaluation of individuals' own spiritual experience as a way of cementing their own authority.
Clearly there are countless people who have had experiences which they believe to be valid or beneficial (even if not spiritual) as a result of the use of mind-altering chemicals. The drug war establishment has refined the art of using devaluation of individuals' assessment of their own experience (i.e. defining all use of illegal substances as abuse) to its own immense profit.
In the end, if you want to play the game of saying that your interpretation is "more right" than other people's own interpretations of their own experiences, you're not doing anything different than what every other authoritarian institution has done throughout history. The mere fact that you're propping yourself up with the dominant religion of your time and place (i.e. scientific materialism) does not change that.
Having said all that, a truly enlightened agnosticism, as I am referring to it here (which is inspired by Stephen Batchelor's Buddhism Without Beliefs,
incidentally) does, in fact, lead one to question one's own experience. The spiritual experience is very much worth questioning. An unquestioning attachment to and reification of a spiritual experience is probably the root of many of the worst horrors of all human history (including all the damage done by the Christian institution over the centuries alluded to above.) Questioning one position naturally places one functionally in an opposing position, and that is exactly the way it should be: if you're going to question your assumptions, don't hold back! But the secret is to be comfortable enough with uncertainty to damp the oscillations that can arise from such a system. Don't swing from one extreme belief to another. Just because the military-industrial complex is killing Gaia doesn't mean you have to be a new-age flake; just because so many psychedelic users become new-age flakes doesn't mean you have to be an angry materialist. There is room for all these (and more) in reality; true sanity requires making room in your head for them, too.