I agree with you all, that it's shortsighted to make these comments. I do look at it from two viewpoints:
One: it is ignorance...but it's in part ignorance based upon an unfortunate part of America's history. The whole black/mixed race, bad hair/good hair aesthetic has been so firmly woven within the very fabric of black culture in this country, that I'm simply not surprised when people go there with it. While curly hair doesn't equal mixed race, it is a likely indicator of mixed heritage somewhere in your background (although we know that most black americans, regardless of complexion, hair texture, or facial features are of mixed heritage). People assign (however misguided) certain preconcieved notions and values to it, and that's very unfortunate. If more women had always worn their hair natural, rather than most of us hiding our texture, I don't think the comments would be so common, becasue we'd be used to the various textures on american women of african descent.
Two: Most people, given a choice, would opt for curly hair as opposed to coily or nappy, undefined hair. As such, I sort of look at those comments akin to when some people make a comment about my weight (like "girl, just shut-up about you need to diet, you are so skinny"). For the record, I am not skinny. (I'm trying to articulate this correctly, so please forgive me if I offend anyone)--while it may irritate me a bit to have folks comment on my weight, I also know that I am in the "favored" category in this regard--ie, given a choice, more people want to be thinner than overweight. So for me, very little folks say about my weight is going to hurt or upset me like people making a negative comment to an overweight person, YKWIM? It's still ignorant and inappropriate, but for me, I don't think the degree of pain is the same. JMHO.