Well, as noted elsewhere, they've created a lot more demand for food that is labeled "gluten-free". They haven't created more demand for food that is actually gluten-free, since they can't tell the difference; lots of people are willing to humor these people by giving them the label they want without going to the effort of taking the gluten out of the food. The same thing happens with "locally sourced".
But unlike "locally sourced", food that has been mislabeled as "gluten-free" is dangerous for celiacs.
As another side effect, the fad people do a lot of work to train everyone to believe things like "people who claim to be gluten-sensitive are stupid". I don't imagine celiacs appreciate that either.