That’s an interesting point. Sometimes people do teach that mindfulness involves “bare attention” or observation without labeling or evaluation, but in fact that’s not really accurate, as is clear from a reading of the Buddhist scriptures on mindfulness.

For example, in the Anapanasati Sutta the Buddha describes the beginning of the cultivation of mindfulness as follows:

“Breathing in long, he discerns, ‘I am breathing in long’; or breathing out long, he discerns, ‘I am breathing out long.’ ”

Similarly, in Insight Meditation as taught by Joseph Goldstein and Sharon Salzberg (among others) at the Insight Meditation Society, they use a technique called “noting” where one attaches a mental label to the object that is most prominent in awareness, which might be “in, out” (applied of course to the breath) or “pulsing, pressure, heat” applied to a physical sensation of pain. They distinguish “noting” from “labeling” which is a much cruder process in which we don’t fully observe our experience because we’ve slapped a label on it. For example we just think “pain” and then don’t analyze all the different sensations that go to make up pain.

“Noting” doesn’t have to overtly verbal, however. When we’re mindful we are aware of different qualities of experience — that this is an unskillful state of mind that we don’t want to encourage, which this is a skillful state of mind that we want to see flourish — but without saying any words to ourselves.

For example in the Satipatthana Sutta it says things like:

“…when feeling a painful feeling, (he) discerns that he is feeling a painful feeling. When feeling a pleasant feeling, he discerns that he is feeling a pleasant feeling.”

This “discerning” is an inherent function of mindfulness.

What you’re warning against sounds more like what the IMS calls “labeling” which leads to us not really paying attention to the texture of our experience because we’ve already put a crude label on it and therefore we think we know what it is.

When we’re really unmindful we don’t even get as far as labeling, however! Instead of realizing that anger is present in our experience we just are angry — and our thoughts, rather than labeling our experience, are about how horrible the person is who did the terrible thing that we’re angry about.

By the way, Alan Wallace has a good article on the distinction between mindfulness and bare attention (which he identifies as manasikara).

Anyway, I hope that’s all helpful.