The people who push this crap, as well as the majority of other 'alternative' medicine, have done a very good job of projecting this image of the evil healthcare industry that is in the business of getting people sick to make money.
The treatments (such as cleansing) have no legitimate studies backing up their claims (a recent double-blind accupuncture study showed no greater benefit to people actually receiving accupuncture to those who were given 'dummy' needles that even to the practicioner appeared to be real, but never actually penetrate the skin), yet people continue to buy into this.
Education in our country is disgusting. Proper nutrition and healthy living need to be taught in schools.
You should ALWAYS be skeptical of any medical treatment. Look for HARD evidence that supports it. Some alternative medicine works, but when it does it becomes medicine.
Oh, and these practices, especially colon cleanses, can actually be very harmful. So be careful. Talk to your doctor (real doctor) before doing anything. You can still do it if they tell you it won't do any good, but it will be helpful to know if it might be harmful to you.