You probably never had a problem with your weight even though you were a lot bigger than other people since childhood days. Most people will accept the way they are but at some time or another you start noticing that you are singled out more than others. Unfortunately this can start in early days at school where bigger children are the target of teasing and snide remarks which can really hurt and even do psychological long term damage. The lack of fat acceptance as early as this can also result in diseases of anorexia and bulimia because of the self loathing of your body.
Everyone has a place in society fat, short, tall, black, ugly, those with different sexual needs, and even the aged. Certain organizations lobby for the rights of specific groups but there are few that cater for fat people. The only one that tries is already discriminatory because it tells you to lose weight in order to be accepted. That is the weight loss industry and the medical fraternity that tell you the horrors of being fat.