Technically there is nothing wrong with gluten. It is a protein found in wheat and some various other plant products. Gluten may be present in some other foods like oatmeal and quinoa by means of "cross contamination" whereby factory processing machines are not cleaned between alternating processing of gluten and non gluten containing foods.
Some people react rather violently to gluten and test positive for something called Celiac. If you are Celiac positive, you avoid gluten and anything remotely resembling it and avoid anything that will even touch it. For example, if you like french fries, you would avoid them because they could be dipped in the same frying oil battered chicken fingers were also dipped in.
The rest of the gluten controversy is in a gray area and not necessarily a medical condition. For example, there is something called gluten intolerance. This supposed condition does not test positive for Celiac but will make someone's life very unpleasant if gluten is consumed. Symptoms may include prolonged diarrhea, bloating, etc. I do suppose since there is no drug to treat this, it is not defined as a medical disorder.
I personally have witnessed more information on gluten. I have worked with people that seem to have withdrawal symptoms from trying to go gluten free. This is still highly controversial but I have witnessed this at least a few dozen times. There are books on the subject such as Wheat Belly by Davis but this book like the others have been highly debated and many people have discredited the findings. Davis did assert that all wheat is GMO and may have high amounts of Glysophate present.
A friend of mine decided to test his blood sugar via a home glucose monitor following the ingestion of white rice and white bread. They were of equal amounts and on separate days. The white bread moved his sugar an additional 30+ points. Keep in mind that this isn't science but a very good lead to create a real study. Nevertheless, after his experiment, he no longer eats gluten.
There is some suggestion that some folks may have a reaction to some short chain sugar molecules associated with gluten. I personally have an intolerance to gluten but for some reason beer does not have that effect. Gluten is surely present in beer but some of the sugars have undergone fermentation and may no longer be present.
The gluten free market is a big industry. Keep in mind that the replacement items may not help with weight loss as many of these ingredients also have a high glycemic index. Gluten free may not be healthier unless gluten does not agree with you.