I think some people do have a medical condition. But "obesity" is just a symptom of that condition... not the actual condition. Other people are just fat because they eat too much and/or exercise too little. I think it is dangerous to just call all obesity a disease.
like it or not the fact of matter lies that obesity is the single biggest avoidable cause of medical expenses. Mental stigma or not a spade should be called a spade
go to Africa and live there for a year. Strangely, your "disease" will be cured