Sorry but you are conflating two different things. Obesity can be a choice and still be a disease. If a smoker gets lung cancer, is it not a disease in their case because they chose to smoke? Does someone who tans everyday and gets skin cancer not have a disease? Why is Type 2 Diabetes, which is the result of obesity, a disease but obesity isn't?
I don't know whether obesity should be classified as a disease or not, I just think your argument is horseshit.