In discussing my weight loss with people, and the addiction model I use for sugar, I am constantly met with a really annoying cliche, "everybody is different". I can pretty universally say though, that if you have a BMI of 45, _universally_ you should not have the caramel goo on top of your Starbucks drink. I can confidently say you should _never_ have it.
The "everybody is different" crowd gets offended by this, and it's tough to draw parallels between sugar and say cigarettes with them. The result of this is that sane nutrition advice gets diluted, or outright rejected. I have said over and over again that the weak strategies put forward by this crowd, like having a regular cheat day are actively counterproductive.
If you are intelligently proposing other approaches, then fine. Veganism can work, calorie restriction can work...etc. However the blanket, brain-dead application of "everybody is different" is bullshit. All you have to do is look around the room at a restaurant. "Everybody is different" is part of the prevailing wisdom, it's part of the bad advice that doctors and media are supporting. All you have to do is look around to notice that whatever the prevailing wisdom is, isn't working.
So where does body positivity come into this? I don't really have a problem with someone making a conscious choice to be fat. I think though, that if you dig into most people's feelings on this, the vast majority of body-positive people have just given up because they have received advice that doesn't work throughout their lives. Doubling down on body positivity because you don't have any other option -- you don't have any experience with approaches that actually work -- it's just sad.
