In this thread: People experiencing somatic issues have relief of their symptoms by placebo diet changes, and are angry when other people point this out.
Also, I have tried a gluten-free diet extensively under the care of a gastroenterologist, in the course of investigation into stomach problems. I've had all the tests you can have, and all came up negative.
The rate of actual gluten intolerance is some 4-5 fold less than the rate of functional disorders - it's nigh on impossible that all those eating a gluten-free diet have gluten intolerance (let alone celiac), but it's extremely likely that they have functional gastrointestinal disorders.