Let me tell you why it's something us plus size folks have needed for a very long time.
It has become a social necessity for obese people to stand up and own their right to be considered a valid part of human life so that they can find happiness in that life, even if they can't be an ideal weight. I think very few people actually understand the level of hatred and ignorance heaped on the obese and how damaging it is to be struggling to have a normal everyday life much less meet society's ideals. We are taught that we are hideous, ugly, stupid, lazy, and worthy of all the hate that comes our way until we reach an ideal weight. The trouble is that it takes a long time to achieve that goal and many of us have health conditions that prevent it from happening at all. As a result we spend a lot of time limiting ourselves because we aren't able to be the ideal size.
We heap self-hatred on ourselves, don't go on dates, don't ask friends out, don't wear a dress and stay in t-shirts and pants instead, we don't wear make-up or don't go out unless we wear it, feel guilty for eating (even if it's a perfectly normal portion and a healthy salad), we tell our lover that we appreciate that they think we're beautiful but really we know we're not, we can't accept compliments because its just "someone being nice". we don't take our kids to parties because we fear other people think we're there for the food, we don't go out for a walk because we know it means being heckled; bullied; and even sexually harassed for it, we are sexually harassed, we are treated like cattle and have our bodies judged out loud as if we are on auction, we have to listen as men heckle each other about how and if they would "fuck that thing", we have to listen to women dictating how invalid we are as women/men, we have to listen to people dictate if we have the right to live our lives as if we were normal, we second guess every single thing we do based on how others will respond, we tear ourselves apart emotionally; mentally; and even physically. We don't have the right to wear shorts in public, to go swimming, to be pregnant and not get judged for it, even people who have no major health issues, despite their size, face serious harassment and even malpractice from doctors trusted to help them maintain their health!
If we don't accept who we are we can't even begin to work on making ourselves fit our own ideals. Why is obesity being treated as if it's nothing to be ashamed of? Because fat people are still people and we really aren't as stupid, negative, unhealthy, lazy and stereotypical as people think we are and it's about time we stood up and said we have every right to claim our lives, even if we aren't what everybody else thinks we should be. I'll bet plenty of 'too skinny' people could tell you the same thing.