I agree, many of these clinics offer treatments that have not been found to be medically sound by the traditional medical community. Some may be better than others and some even dangerous as you mentioned. The real question is why have these clinics grown in such numbers.
Of course because people like to think there is something they can do for an illness, though no known cure may exist. People like to feel like they are taking charge.
But the second reason I believe is essential to address: Many people feel abandoned by the present medical system. They do not receive the personal care that they find in these alternative establishments. Doctors often say, "You have only a few months to live," and then the patients go on to outlive these predictions. Patients don't like having a pronouncement of doom given to them. I don't suggest that doctors should conceal information from their patients. I do believe, however, that the healing process has an increased chance of succeeding when the patient is optimistic and feeling positive.
Norman Cousins expressed all of these views very clearly in his book "Anatomy of an Illness." Since its publication, numerous studies have linked one's state of mind with one's physical well-being.
If American doctors would begin tending to their patients' emotional needs as well as their physical needs, they may find that fewer patients will run south of the border to have these needs met.