Theories behind food sensitivity fads

Ever find yourself wanting to yell, while waiting in line as someone ahead of you figures out what the gluten-free, soy-free, dairy-free options are, "Oh, just order the salad! You diet-demanding people are everywhere!"? I know that you, being a good Minnesota nice person, would never even think such a thing, right? Wink, wink, nudge, nudge. Trust me, living the dream of diet dissection is not fun for us, either.