I sort of agree with you, but a lot of illnesses are actually just vulnerabilities to certain other things. For instance, celiac is considered a disaease, but if a celiac patient never lets a grain of wheat pass their lips, they'll suffer no symptoms. As far as I know, AIDS won't kill you if you manage to avoid ever being exposed to any other infectious agent. A clinically significant phobia of spiders would not cause you any discomfort in a spider-free environment. Why couldn't we characterize "susceptibility to assorted causes of death" as an illness of its own?
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.