You seem to be assuming that the health conditions and costs commonly associated with obesity are all primarily caused by obesity. I'd suggest you consider the possibility that obesity is just as likely to be a symptom of poor health as it is to be the cause of it. On this point, there are plenty of people who aren't obese who have cardiovascular disease, diabetes, etc.

There's a lot we don't know about the human body, but based on what we do know, it's asinine to believe that folks can eat horribly and live sedentary lifestyles without serious consequence. That, however, is what magic pill research effectively promises.