Q: Why do you expose magic tricks?
A: Well, I happen to know people with stress problems, AIDS disease and people with bad habits that found in magic the relieve emotional "medicine" for their problems, not because they were trying to deceive people, but because the practice and attention that some of these illusions may take. Also creating Illusions and/or techniques for a trick can increase skills, attention, and memorization; it is a good mental exercise, also an art that can keep people busy and away from problems and/or bad habits. Of course, misusing this art can be a wrong way to take advantage of your skills as any other hobby or career may be (not just magic).
Other reasons are also associated with ignorance and the consequences of it (as you can read on the rest of the Question & Issues).
Part of the magic community is divided on this matter since some magicians are not too concern with magic exposure because they realize not every layman cares about the method.