Here's an example from work today that fits this issue perfectly:
The patient was a seven year old female with a diagnosis unrelated to weight. She weighed 70 kgs (155 pounds). As a reference, the 98th percentile for a 7 year old girl is 70 pounds. The patient refused to do simple things for herself- such as help reposition herself in bed, feed herself, and wipe herself after she had a bowel movement. If I told her she had to help or had to do something for herself, she would whine and complain that she "can't do it" or she "didn't know how."
Instead, her mother would do these things for her. Her mother also brought her extra snacks and juices (mom reported the child drinks up to 64 ounces of juice per day). When the child refused to eat the meals that dietary had prescribed for her, the mother would bring her bacon and sausage, grits covered in butter, McDonald's cheeseburgers and french fries, cookies, etc. I don't think she ate a vegetable all day.
It was extremely frustrating for me to take care of the patient when the child was acting so helpless and the mother was enabling her laziness and poor eating habits. I'll freely admit that I had more than a few judgmental thoughts about the family. But what really irritated me was not that the child was morbidly obese, but the attitude that accompanied it. The weight wasn't the issue- it was the fact that the patient (in this case, the patient's mother) refused to acknowledge there was a problem or invoke change, despite education from our nutritionists.
I realize that this situation is not the child's fault. Seven year olds cannot go out and buy McDonalds themselves. They can't drink a gallon of juice per day unless someone is bringing it home for them. They don't get away with doing nothing for themselves unless someone is willing to do everything for them. So my bigger issue was with the mother, not with the child. While the child wasn't admitted for a condition directly related to her weight (but she did have a history of hypertension and obstructive sleep apnea) a good diet is very important in the management of her condition. And even though she wasn't in the hospital for a weight issue, there was no doubt that her weight was directly affecting her medical care and her recovery.
I suppose my point in all of this was that, for many people in the healthcare field, it's not the patient's weight that causes them to have prejudice or be judemental- it's the attitude of the person who is overweight. Or, it's the health care worker's repeated exposure to the attitudes that I described above that cause them to have negative associations.
Finally, even if you don't have a medical problem that's caused by being overweight, the weight can still be a factor in the management of that condition and the overall health and recovery time. A hysterectomy may not be related to weight, but a morbidly obese patient who can't get up and walk after surgery is at much greater risk for complications and much more likely to end up staying in the hospital longer or going to a SNF. So if it wrong of the gynecologist to bring up weight, even though it isn't directly related to the issue at hand?