I have some more thoughts about why doctors are so willing to blame a fat patient's weight for their medical problems, rather than treating them the same as a thin patient. Actually I have two I would like to share.
One, doctors are overworked and often seeing dozens of patients a day. It is easier and less time consuming to say "lose weight" than run tests and go through a complete diagnostic criteria. And to the doctor, it's one less patient they have to deal with. They can just dismiss and shame a fat patient and move on to the next without fear of discrimination accusations or lawsuits.
Two, it's about control, ego, expectation. When they blame a person's weight, they feel as through they have found the problem and can "fix" it. It's much harder to deal with a problem without a clear and obvious answer. But truthfully, even with all the advances in medicine, there are many things we don't know/understand about the human body and illnesses. It's much harder for doctors to admit they don't know something. They and possibly patients expect that they will be able to find the problem and fix it. It's a big expectation and responsibility to live up to. Blaming someone or something else takes any responsibility out of their hands - it removes the pressure and expectations.
Now, this doesn't mean I feel fat patients (myself included) should not take responsibility for our own health. We should try to be as healthy as we can - at any size. However, fat patients should not be shamed by doctors nor accept a lesser quality of treatment than their thin counterparts.