We are supposed to learn to take care of our bodies--to treat them right, fuel them right, and use them right.
I think people deep down feel shame that they aren't doing it the right way.
But as others have said, some people have tried and haven't been able to make it work. This is the next best thing--it is better than letting disease run its course.
I think the truth is somewhere in the middle. If you are taking the drug and also working to improve eating/exercise habits, good for you. If you are taking the drug and still eating Doritos and sitting on the couch, you probably should feel sheepish.