I think the article is interesting, but in part is a problem of semantics and not concepts. That is, if we remove "mysticism" as a label all together, that does not remove the concept people have of "that bunch of stuff that seems cross-culturally similar in significant ways and involves reaching out to some extraordinary experience."
The reason many people, including scholars, see an underlying unity in mysticism in various traditions is that mystics themselves often see it. Yes, mystics' experiences differ and how they interpret that varies according to their cultural and religious traditions. However, most people who have significant mystical experiences over time, particularly those that pursue it routinely, are aware that their attemtps at interpretation and communication of their experiences fall very much short of the actual experience. As IL was saying, it cannot be adequately described, least of all in a scholarly manner, and the closest many people often feel they come is through art or poetry, which allows a transfer of some of the experience without quite so much filtering.
While on the surface, many mystical traditions and experiences may seem quite different, "mysticism" is simply referring to the underlying commonality in them. This needn't be from the perspective that they are, indeed, caused by an experience of a transcendental reality as the author states. In fact, if it were based on that assumption, the term would not be used by most social scientists. Having had mystical experiences myself, I do believe that these arise from interaction with an extra-ordinary reality, which I refer to as God or the Divine, but acknowledge other ways of expressing it. However, as an anthropologist, I would not base a cross-cultural comparison on that assumption. Rather, one can look at a common type of experience based on how it affects the humans involved. Altered states of consciousness, paired with various sensory and physical sensations, are fairly common cross-culturally in these sorts of experiences. Whether you argue these arise from interaction with the Divine or simply from certain ways the brain is functioning, it is remarkable that in many cultures worldwide (including many shamanic traditions), people attained certain common experiences (such as auditory and visual hallucinations, significant changes to heartrate and breathing patterns and pain response, feelings of oneness or unity, etc.) through certain widespread practices (including fasting, exposure, spinning, drumming, chanting, taking drugs, etc.). There ARE significant widespread behaviors and ideas that are cross-culturally observable and these are what most social scientists refer to as mysticism (generally in reference to world religions) and shamanism (generally in reference to shamanic traditions).
To say that these commonalities are to be disregarded due to cultural and religious variety in their interpretation and symbolism is to take, I feel, an extreme position in antithesis to reductionism. Yes, we do not want to reduce all "mystic" experiences to one blob of non-culturally-defined stuff, but we also don't want to ignore significant elements of human experience that are widespread in order to disintegrate into a position that does not allow that humans, as a whole, share anything in common. In fact, it seems particularly important to our understanding of what makes humans human that mystical experiences are so widespread. Intellectually, this points to a unique way that human brains function, and like art and music, is such a uniquely human trait that has no immediately apparent evolutionary function. Of course, for many people (but not a scientific position), this also points toward a reality of underlying transcendent reality, which people cannot fully grasp but can experience.
I think what the author confuses is the first position with the second. The author assumes that scholars are lumping together certain practices and experiences as "mysticism" AND assuming they are borne of interaction with the Divine. In actuality, many scholars I know are agnostic or atheist and they are lumping together certain practices and experiences as "mysticism" without reference to any transcendent whatsoever. They are lumped together because of their common traits. Of course, they vary by culture and religion. So do all the other things we lump together in order to theorize about them. For example, capitalism, socialism, Christianity, Buddhism, horticulture, pastoral, magic, witchcraft... the list goes on and on and on. The capitalism of Ghana fish markets isn't much like the capitalism of Wal-Mart. (Wait, but Wal-Mart isn't REALLY pure capitalism... I digress
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The reality is that in theorizing about people, we either agree to simply study each culture and religion individually and never make any statements about humanity as a whole or what processes lead to what types of societies (yawn, boring, and not theoretically all that useful) or we sacrifice some of the distinctiveness of each in our quest for understanding underlying processes of humanity and society. Heck... by extension, the same could be said of biologists, who have to draw lines in the sand and lump species together into higher categories. It is the nature of categorization to be slightly inaccurate, but categorization is still a useful way to look for patterns.
As for my answers to the questions...
I preface with my favorite definition of religion (also a tough one to define).
1A. Religion is human transformation in response to perceived ultimacy. Ultimacy conditions and gives meaning to all of existence.
1B. Mysticism is the group of behaviors designed to grant direct experience of perceived ultimacy.
2. A mystical experience is one in which the person has a direct interaction with perceived ultimacy. I agree with IL that this surpasses our communicative abilities, so while mystics tend to easily recognize commonality in others' mystical experiences, no one can adequately express what they have experienced.
3. Two answers to this...
As a social scientist, you judge a mystical experience by your definition, but you are always relying on the interpretation and expression of the mystic. So, in fact it still goes by to IL's observation that only the individual person can deem an experience mystical.
4. Yes. And yes. I explain a few above but could provide a list of behaviors, emotions, and thoughts that are commonly found cross-culturally in mystical experiences. Interpretation of experience varies widely, but the underlying behaviors that lead to mystical experiences and the physical and sensory manifestations are observable and found throughout the world.
