Respectfully, I think the point some people have (myself included) is that while it is OK (actually fine I guess) that overweight people have a "positive body image", it is not HEALTHY. In any way, shape, fashion or form. None. The adverse health effects are numerous, proven & undeniable.
If a "large" person believes that their lifestyle is good, they are fooling themselves. Denial of an unhealthy lifestyle does not make it ok. I link them into the same category as smokers, alcohol & substance abusers.
The thing is that, in most (but not necessarily all) cases, this is due to a sedentary lifestyle & an unwillingness to make the right decisions for a healthy lifestyle. It's easier to cry for "acceptance" than it is to lose the weight. That would take work.