www.quackwatch.org should be essential reading for everyone ....
I actually have a couple of the eye-related reports (iridology and eye exercises) printed off and sititng in office so that i can give them to anyone that wants to know about them.... they are BS, but a lot of people tell them that they work.....
This site helps people make an informed choice about what is best for them personally.....
As for Chiropractors..... there is no such thing as prophylactic back care.... either you have a back problems, or you dont..