A part of me wants to like the fat acceptance movement, it really does.
Unfortunately I see far too many people in those movement who are just downright unrealistic. They demand that society see them as beautiful. Beauty is subjective, but a large part of it is an instinctive mate selection. Obesity can often cause complications in fertility, during pregnancy, and birth and so people have a natural instinct to avoid such mates. The same is true fro underweight people.
This does not even begin to mention how they demand they are healthy but suffer from many obesity related medical conditions, particularly join pains. I agree that BMI is inaccurate, and that it is possible to be heavier and healthy, but the majority of people in the fat acceptance movement I have seen are monstrously obese.
Then they use things like claiming that because of hypothyroidism or cushingtons you cant assume that fat people simply eat too much and dont exercise enough. Which is fair, until you take into consideration how rare those disorders are. The majority of obese people dont have any medical reason for their weight, but the fat acceptance movement gives them validation to continue their often extremely unhealthy lifestyle.
Loosing weight is hard, it is painful and our bodies are evolved to do everything in its power to keep eating as much high energy foods as possible. Our Brains are giant energy sinks, so we have evolved to try and consume as much energy as we can to keep out large brains functioning at peak capacity. In many regards high energy foods are like drugs to our brains. That is why we crave them, and especially why when going on a diet, our brains make us crave them even more. It even starts creating justifications for those foods, just like an addict would in any other withdrawal scenario.
The golden rules of weight loss have never really changed. Energy in must be less than energy out, metabolism and hormones aside, the laws of thermodynamics are absolute. Sure people need to understand that 100g of sugar is different to 100g of lettuce leaves because they both have different energy potentials. Even if you only eat lettuce, eat enough to exceed your energy output and you will still gain weight.
Back on topic though, I just feel that the fat acceptance movement is far more harmful than helpful.