Many of the prophets of old would probably be labeled as mentally ill today. The visions of prophets such as Ezekiel or Joan of Arc would have rendered a diagnosis of schizophrenia and a trip to the funny farm. In general, the West has at best downplayed the visions of the mystics, prefering the more concrete depictions of rational and critical thinking. Empirical evidence is the bastion for determining reality, and anything outside of this context is suspect. Calling deviance madness is a good way to nullify it.
Yet what is irrational about religion or spirituality? Those in religious circles who subscribe to rationalistic, literal interpretation of their scriptures should remember that the belieifs they hold have their origins in mystical revelation. Suspicion of revelation outside of the prescribed text belies the fact that no religion is provable, therefore all is mystical, regardless of the history and tradition of the creed.
For example, many extreme fundamentalist Christians discredit any doctrine or practice that seems in any way extrabiblical. Some examples of this would be the ordination of women or the use of New Age concepts such as silent meditation. The justification for this is that in the Bible, all revelation has been revealed, so anything that seems not to have a literal mandate to it must be false doctrine. Yet orthodox Christianity was deemed heretical during its early years by the Roman government. Salvation through the reserrection of Jesus of Nazareth, a prolific concept throughout the writings by Paul of Tarsus and the other New Testament authors, is in itself exrememly mystical, and has little logic to its basis. Scriptually, this concept, which is at the heart of Christianity, has its roots in unorthodox interpretaions of Isaiah and Jeremiah. The Jewish nation was expecting a Messiah on the order of King David, not a man who preached about a kingdom not of this world. Adding to this the paradox of Jesus being both human and divine, and you have a doctrine that would seem ludicrous to any empiricist. A rationalist, literalist approach to Christianity is nearly impossible; Christianity is mystical to its core.
Visions, revelations, and prophecies in and of themselves do not mark a person as mad or in need of psychiatric help, regardless how uncomfortable it makes others feel. Scooting the visionary under the carpet, disowning his theories outright as delusions, or writing him off as evil because one disagrees with him denies the power of the spirit. If all hallucinations are madness, then what becomes of imagination? Are the composers, the mathemeticians, the scientisis and the artists nothing more than madmen? Should they be locked up before they start, just so that others may remain comfortable in the paradigm of the tangible? The line between creativity and what is considered to be madness is an indelibly fine one. The border is set and defined by cultural biases, rather than any real definition of madness.