Well, y'all, I covered that particular topic over a month ago, but it seems to be all the rage now. So let's do this thing.
Dividing people in acceptable and unacceptable examples of their oppressed demographic is a time-honored tactic by oppressors. If you can get at least part of the group to turn its back on the rest, by way of convincing them that the oppression is somehow their own fault, and that it can be relieved by behaving in a particular way and alienating those who do not, well, doesn't that seem a perfect strategy for not just getting as many of them to behave the way you want them to, but also to assist you in oppressing their own demographic?
This is a well-beaten path, and we need to look to the experiences of those who have gone before us in pursuit of human rights to guide us. Civil rights activists have long known that when oppressed persons engage in behaviors (such as "acting white") to please their oppressors and mitigate their circumstances, the only thing that changes is the form of oppression. You are not truly free if you must behave in particular ways in order to avoid being abused.
We must also not fall into the trap of believing that those who abuse us have our best interests in mind, no matter what they claim. The abuse is easier to accept when we believe we deserve it, and abusers frequently try to convince their victims that the abuse is the victim's fault, and they wouldn't be abused, if only they would have done certain things. The truth is, abusers have no right to abuse, and they do so because it satisfies some desire or need in them--NOT because their victims deserve it. If the victims did not have a certain behavior or quality that the abuser focuses upon, there would be some other behavior or quality that the abuser would use an excuse.
None of us deserves the poor treatment we get for being fat. Every single one of us deserves basic human rights and dignity. What we eat, how much we exercise, our vital stats? Those aren't even a factor. Being a living, feeling being should be enough to warrant dignity. Don't stand for any less.