One is never ill in general. One is always ill in relation to some activity. It is not cancer that makes me ill. It is because I cannot work, or run, or swallow that I am ill with cancer. The loss of function, the obstruction of activity, cannot in itself destroy my health.
I am too heavy to fly by flapping my wings, but I do not complain of being sick with weight. But if I desired to be a model, jockey, or dancer, I would consider excess weight a disease I would like to be cured of.
Carse, Finite and Infinite Games, 3.56
There was some talk here about height taxes, but there's a better solution - redefine shortness as a treatable condition and use HGH to cure it. They even got FDA on board with that, at least for 1.2% shortest people.
Unsatisfactory sexual performance became a treatable condition with Viagra. Depression and hyperactivity became treatable conditions with SSRIs. Being ugly is already almost considered a treatable condition, at least one can get that impression from cosmetic surgery ads. Being overweight is universally considered an illness, even though we don't have too many effective treatment options (surgery is unpopular, and effective drugs like fen-phen and ECA are not officially prescribed any more). If we ever figure out how to increase IQ, you can be certain low IQ will be considered a treatable condition too. Almost everything undesirable gets redefined as an illness as soon as an effective way to fix it is developed.
I welcome these changes. Yes, redefining large parts of normal human variability as illness is a lie, but if that's what society needs to work around its taboos against human enhancement, so be it.