There is no actual evidence that gluten is in any way bad for 99% of the American population. A small fraction of Americans (less than 1%) are allergic to gluten, and must avoid it because they’re allergic. To the rest of us, gluten is harmless.
That said, a gluten-free diet means eating less processed junk food, which really is good for you.
The Rationalist Conspiracy 
I forget who pointed this out (probably several people) but it seems likely that gluten free and paleo diets serve as crypto-low carb diets for SWPLs. That is, traditional low carb diets are too low status.
I guess here’s where I’d go with it:
‘Most people won’t benefit from avoiding gluten. Even if you’re feeling unhealthy, avoiding gluten probably won’t help. However, assuming you’ve tried all the high probability interventions (a diet full of fresh foods and not too much carbs/fat, exercise, lower stress, etc) it’s not a bad place to start. In fact, of the set of cryptic/low-probability interventions, it’s probably near the top of the list in terms of expected benefit.’