Medical diagnosis of gluten intolerance is pretty rare, because as I mentioned above, the diagnostic procedure is very unpleasant - mostly it's diagnosed by the symptom pattern. If you think only people with a formal histological diagnosis have a "right" to the label you're dismissing a hell of a lot of people with real illness and with more common sense than the average about what the medical profession can't do for them. What exactly is the point of getting a formal diagnosis that only tells you what you already know and doesn't get you any better treatment?

You get somewhat similar issues with Lyme disease. A lot more people have it than have been diagnosed, because the diagnostic methods are pretty rubbish (not harmful like those for gluten intolerance, but they have a large proportion of false negatives). So people guess. Some of them guess wrong. The results are not good whichever way they're wrong (you either miss out on the most effective treatments or waste money on less effective ones), but it's hard to see an easy fix.