As I mentioned at the beginning of this series on mysticism, a number of criticisms can be leveled against it and some of them are legitimate. Here are some of the more blatant ones.
The "John the Baptist" fallacy
John the Baptist was a holy man. He lived in the desert, wore strange clothes, and ate strange food. But living in the desert, wearing strange clothes, and eating strange food does not make you holy. Dedicating your life to showing people Christ, the way to God -- that is a holy life. Strange food and strange clothes and deserts have nothing to do with it.
The "eccentric" fallacy
Some very holy people, turning their backs on the world to serve God, are seen as eccentric. That does not mean that being eccentric is a sign of holiness. Turning your back on worldiness to serve God is a sign of holiness. Acting bizarrely, speaking strangely, or having odd manifestations are not in themselves anything to be proud of. A follower of Christ does not call attention to himself or herself but to Christ, and actively avoids doing things which bring discredit on the name of Christ.
The "unusual experience" fallacy
Mysticism is not defined by a strange experience of something you have never seen before and cannot understand. It is awareness of God's presence in the things you see every day. As Jacob said in Genesis, "Surely God is in this place, and I did not know it." To know it, understand it, appreciate it -- these are the tasks of a mysticism that is healthy and well-grounded in reality.
The "holier than thou" fallacy
Mysticism is not a special elite club dividing Christianity into haves and have-nots. Mystical experience is allowing yourself to dwell on the holy realities of God. There is not a Christian who does not experience this to some extent. Anyone who uses spirituality as a form of one-upmanship just doesn't understand Christian spirituality very well.
The "ecstatic, cheerful, glad" fallacy
Spirituality encompasses all of human experience, not just the happy times. Spiritual experience can involve profound gladness or ecstasy. It can also involve deep sorrow, shame and repentance, exhaustion and despair, or an aching knowledge of distance from God. Most often of all it involves an emotionally low-key state, a quiet time of pondering. Honestly, many people have such hyped-up expectations that they find the experience itself disappointing. It is dedication that makes people return to meditation again and again. It is apparently a common temptation to try to manufacture "ecstasy". This makes for a shallow and forced experience that is not genuine.
"Heart and Soul" v. "Mind and Strength"
As mentioned in an earlier post, systematic theology tends towards forgetting heart and soul in favor of mind and strength; this has been a weakness of systematic theology that leaves a distorted, not-fully-human, not-fully-godly result. Mysticism often has the opposite tendency to forget mind and strength in leaning towards heart and soul. Likewise the result of the split is not fully human and not fully godly. Mysticism can tend towards the emotional and forget discernment; it can tend towards the mysterious and forget the truthful. Our approach to God cannot afford to be merely "balanced" bouncing between extremes (say that five times fast); it has to be integrated. Until then, our "systematic theology" will be dry and our "mystical theology" will be a portrait painted in swirling pastels without form or substance.
False goal of "being spiritual" instead of following Christ
Mysticism cannot be a goal; it is a means. If we lose sight of Christ, then we easily get lost. Mysticism, rightly used, is another way to fix our eyes on Jesus, the author and perfecter of our faith.
Some of the problems associated with mysticism are not unique to mysticism. In too many religious endeavors, people forget that even religion and holiness can be misused. There is a temptation to be undiscerning when people have their hearts in the right place (or did in the beginning). There is a forgetfulness of sound guidance and good advice in favor of excitement. Mysticism may be especially prone to these problems when it has to assert its way over against an "intellect-only" approach. Some beginning mystics naively (and very wrongly) think of the intellect as only a "criticizing spirit" instead of their God-given tool for discernment in these things.
It is dangerous to seek after "the mystical experience"; real mystics do not seek that but seek God. In real mystical experience, all kinds of emotions may attend you. It's a beginner's temptation in religion to try to be always only happy. A good look at Scripture will show this as shallowness, not maturity. The "experience" depends partly on each person's temperament, partly on the particular meditation of the day, and partly on whether you're well-rested enough and free enough from distraction to really dwell on what you are considering. Some may dwell on the goodness of creation, a passage of Scripture, an event in the life of Christ, regret over some evil they have done, pain over the troubles in their lives, or "whatever is true and right and noble" as the case may be. Seeking knowledge and love of God is the right aim.