I found this organization which, I think, says it very well.  
"Founded in 1969, the National Association to Advance Fat Acceptance (NAAFA) is a non-profit, all volunteer, civil rights organization dedicated to protecting the rights and improving the quality of life for fat people. NAAFA works to eliminate discrimination based on body size and provide fat people with the tools for self-empowerment through advocacy, public education, and support.

Fat people are discriminated against in all aspects of daily life, from employment to education to access to public accommodations, and even access to adequate medical care. This discrimination occurs despite evidence that 95 to 98 percent of diets fail over five years and that 65 million Americans are labeled “obese.” Our thin-obsessed society firmly believes that fat people are at fault for their size and it is politically correct to stigmatize and ridicule them. Fat discrimination is one of the last publicly accepted discriminatory practices. Fat people have rights and they need to be upheld!
NAAFA will be a powerful force for positive social change. Using our collec­tive will, talents and resources, we will improve the world — not just for fat people, but for everyone.

Visit their site at:  http://www.naafaonline.com/dev2/about/index.html

NAAFA’s message of size acceptance and self-acceptance is often overshadowed by a $49 billion-a-year diet industry that has a vested economic interest in perpetuating discrimination against fat people. Without active financial support from people like you, NAAFA would not exist and could not fulfill its crucial role defending your rights. While it is an uphill battle to achieve our goals, together we are making a difference.