I don't really see the connection between being healthy and being fat. Of course, it depends on what we mean by "fat." For me, I understand fat to mean obese or close to it. There is nothing positive about this. I don't feel good about my joint pain, sleep apnea, and greater chance of developing heart problems, arthritis, diabetes, and cancer.
I am not saying the fat people are bad people. I just can't get over the feeling the calling for fat positive imagery in the media is like calling for smoking positive imagery. I remember when there was virtually no public place you could go without having to deal with everyone's second hand smoke. There was a massive and very successful campaign to reduce smoking in the US with understanding that the diseases caused by smoking were a threat to the collective health of the nation. I would like to see a similar campaign to fight obesity. Let there be a nation-wide mobilization to educate people to the dangers of obesity, to encourage people to take control of their bodies, their health, and of their very lives.
Again, this is not a question of morality or judgement but rather one of health. Unless my understanding of the health risks of being fat are wrong, and please correct me if it is, fat postive imagery is not in the interest of public health.