It turns out that further scientific studies have now clearly shown that there are compounds that have higher concentrations in gluten-containing grains that cause digestive distress in a significant fraction of non-celiac people who report digestive distress correlated with gluten-containing foods.
Which is to say, yes, technically it's not the gluten per se, but "contains gluten" is an excellent proxy for containing the actual problematic compounds when one is eating commonly-available foods rather than highly-abnormal things created for scientific experiments. And "gluten-free" is also a good proxy for not containing those compounds in significant amounts.
Or, in small words, science just showed that eating normal food that contains gluten causes them to have problems.
I further note that this is something we already knew, except for the scientifically controlled study part of it. Because science is about improving theories until they match all of the relevant facts, not about discarding ones like "the person in front of me says that eating things with wheat flour or other gluten-containing stuff in it makes them sick" just because it's not conceptually convenient. The science part is that some scientists looked at the two facts of non-reaction to gluten in pure form in precise studies, and reported reaction to gluten-containing foods in people's normal lives, and said "there must be something interesting here," and found at least one piece of it.
As opposed to the unscientific people who assumed that the facts in the controlled studies must mean that the facts in normal lives were imaginary, and did nonconsensual experiments on their friends or family to "prove" that the latter facts were imaginary, after which their friends and family learned interesting and important things about these people's trustworthiness.
Crossposted from Dreamwidth (original here), with comments. Comment here or there; comments here will eventually be duplicated to there.