Mysticism is the interior heart and soul of religion just as, conversely, religion is the body and clothing of mysticism, its outwards and external aspect. The former is an entirely personal and private experience to know God (by whatever name) directly. The latter sets up God as an external divine power to enter into a relationship with. Therefore, the religious man tends to pray, whereas those mystically inclined prefer to meditate.
Both mysticism and religion attract nutters and lunatics (so also does science: the Harvard neuroscientist who proposed cloning a Neanderthal man from fossils is one example). However, a neurotic mystic or a fundamentalist religionist in no way denigrates the value of mysticism or religion any more than, say, a collapsed bridge degrades the value of civil engineering.
Mysticism tends to attract neurotics rather than fundamentalists. Conversely religion tends to attract fundamentalists because in addition to its personal aspect, religion also has a social and organizational aspect with politics and power going hand in hand with control, corruption and violence.
Therefore, a religious fundamentalist is a far greater danger than a neurotic mystic: the former endangers society through violence and dogmatism whereas the latter harms only himself and his deluded disciples.
Another point is that deeply religious people and mystics, as well as fundamentalists and neurotics, report hearing voices and seeing visions. The outward expression from both groups can be remarkably similar, except that in the former the intimation comes from the Higher Self or Overself, whereas in the latter case it is the fantasy making characteristic of the mind. It is no easy matter to distinguish an authentic communication from a delusional one because both have an appearance of the real. But to use an analogy for the latter case, an image of a person in a mirror looks very real; but break the mirror and you only have broken glass, not a broken person.