When celiac sufferers ingest the dreaded stuff, the immune system responds by attacking the small intestine, which leads to a sort of intestinal baldness. Villi, hairlike protruberances that line the small intestine, absorb nutrients into the body, but when people with celiac eat gluten, the villi get flattened or otherwise damaged, making proper nourishment impossible.
If left undiagnosed, celiac can lead to massive malnutrition, wasting, and even death. But people with celiac can lead perfectly healthy lives provided they forswear gluten. Which means no beer. Which is, frankly, unacceptable.