Answer:  I get this type of question quite often.  Not only for
gluten, but also dairy, nuts and other foods that trigger allergic
reactions or intolerance.

For those with diagnosed allergic conditions to gluten (the protein
component found in wheat, barley and rye), or other types of food for
that matter, it's a no brainer that you need to craft a diet to avoid
them.  Although food labeling is getting better at identifying food
allergens for consumers, it is neither rock solid, nor guaranteed.
Gluten is used quite extensively in processed foods as a stabilizing
agent (ex. ice cream, meat substitutes, etc.), so it can be hard to
detect if the manufacturer is not adhering to FDA labeling
standards.

For those with intolerances, it's not a potential medical red flag if
you eat the identified foods, but it sure makes life uncomfortable.
Those with lactose intolerance certainly understand this (i.e. lactose
intolerance).

To clarify the difference between an allergy and intolerance, an
allergy triggers an immune response in the body causing the release of
histamines and other defensive agents (a.k.a. an allergic reaction).
An intolerance is an adverse reaction that does not involve the immune
system. It causes reactions such as gastrointestinal distress,
headaches, hives, bronchial/sinus irritation and other such
discomforts.  Whereas allergic reactions typically require the use of
antihistamines and other pharmaceutical antidotes, intolerances
subside after reactions run their course.

Now to answer the question.

If a person is not diagnosed with celiac disease or gluten
intolerance, and doesn't suffer from any of the related adverse
reactions, I recommend not avoiding foods containing gluten.  Taking a
holistic approach, barley, wheat and rye are nutrient-dense.  Not only
do they provide some protein from gluten, these grains are also an
excellent source of fiber, lower glycemic carbohydrates and essential
minerals.

The key word is "minimally processed".  Certain food additives used in
shelf stable, mass consumables may be the culprit.  Think about this
way:  When components of food, such as gluten, soy, dairy, etc. are
stripped out, refined and concentrated into a food additive, they may
be not be recognized by our bodies, and therefore trigger an immune
response.  But when eaten in whole or minimally processed form, they
are digested, processed and utilized/disposed of without incident.

Finally, for individuals trying to link a condition or reaction to a
food or food component, a simple approach is to remove all forms of
the suspected food from the diet for a period of 1 to 2 weeks.  If
symptoms subside and you feel better, it may be a strong case that the
food and your body are not compatible. Otherwise, there are a number
of tests that medical professionals can perform to help diagnose food
allergies and intolerances.