I read a lot of fat acceptance blogs because I'm on board with body acceptance and people being allowed to live their lives (and deal with the consequences) in any way they choose. That being said, I wish that the fat acceptance advocates would separate their anti-diet agenda from their fat acceptance agenda. It is possible to accept your body as is, but not be against weight loss as an idea. Many people would want to lose weight even without the social stigma attached to being fat because it generally makes movement easier, reduces stress on joints and bones, and improves energy.
Apparently, "no diet day" was several days ago and a lot of the fat acceptance blogs took this as an opportunity to offer up "evidence" and opinions that dieting (as in calorie restriction or food control) is bad for you. There was everything from the idea that dieting will cause cancer and heart disease to the notion that it will make you gain weight. All of these conclusions are correlation and causation errors, but they are pointed at nonetheless as a means of supporting a "pro-fat" agenda. Restricting your eating doesn't cause you to gain weight, but many people do regain the weight they lose and more. That is a correlation, not a causation. Also, being overweight and changing your eating habits to lose weight causes stress which leads to a variety of illnesses like heart disease, cancer, and diabetes, but the dieting does not cause these diseases.
At any rate, I didn't observe "no diet day", because I think the idea is silly and frankly I have no urge to abandon my eating plan for a day. I don't need or want permission to overeat by some made-up international holiday. I'm not a diet and exercise zealot by any stretch of the imagination, and I think people's eating habits are their own business and their body size isn't the concern of anyone but themselves. That being said, I think that fat acceptance advocates aren't doing themselves or anyone else any favors by asserting the equivalent of "dieting kills."