Some people are happy being large, the only reason we judge it badly is because of what is considered a social norm, a social norm established by the media, ever wondered why most women in old paintings are chubby? Its because that was what was considered attractive.
But that's not your point.
Fat people can be disabled, weight can be a dissabilty, limiting movement drastically and cannot usually be lost the normal way at that stage, it becomes a medical issue.
It is not always the person's fault, comfort eating, (and yes it is as real as anorexia), is an issue, as are other medical issues. But sadly in truth the majority of fat people are just that, fat. However, you don't know why a person is large so its not right to judge, nothing is black and white.
Weight at a certain stage or caused by other medical issues or mental issues is a disability, the only reason people are harsh is because they view fat people as abnormal because they don't fit a social norm created to make money