There shouldn't have to be a fat acceptance movement in the first place. It is in response to fat shaming.
If fat-shaming is done for aesthetic reasons then why isn't there "ugly mother" shaming? Ugly is far worse than fat, isn't it? But then, there are far more ugly men than fat women, and we wouldn't want to upset the men by judging them by their looks.
If it is a health issue, why aren't we directing the same amount of disdain to drinkers, smokers, drug addicts, and lazy skinny people who never exercise? When is the last time a drinker was shamed in a national mag for indulging in unhealthy behavior? Or a drug addict shamed for having no self-control? Instead, we have consumer products telling us which alcoholic beverages are "less" toxic than others and an entire industry developed around coddling the drug addict. I suppose if there was more money in fat people, they'd get more respect.
Fat shaming is just another form of our culture's obsession with misogyny. Break them down so we can keep them in control. And the fashion industry is one of the worse misogynistic offenders.
No, the fat-acceptance movement has not done more harm than good. It hasn't done enough in my opinion. They should be driving the businesses who perpetuate such messages out of business. Once you threaten the money, your acceptance follows quickly.
However, I think you are missing a piece of the puzzle that doesn't even get addressed in many of the other conversations on this topic. The vast majority of people who die from heart attacks, coronary disease, and even diabetes are not obesely fat. They are actually only a couple of kilos over the national average in most cases. So if we can consider these people unhealthy because of their weight, then we can consider half of the population unhealthy.
However, somehow the conversation does not revolve around the "average weight" for us which is proven bad, but only people we consider "fat people." I wonder how that would look applied to other areas of life. A person who murders five people has a serious problem, but a person who only murders two people is acceptable because at least he hasn't murdered five.