Earlier quoted context omitted.
I don't know why you point out that it's impossible to falsely diagnose cancer in a patient who has cancer. Surely you agree that it's also impossible to falsely diagnose autism in a person with autism? But perhaps your remark simply reflects a metaphor stretched too far. I realize that you are not the original commenter who alleged that the term "autism" was being thrown around too lightly, but you're happy to agree…
In my opinion, people are different. Attributing differences to disorders is not productive, and tends to lead to things such as medication and expensive treatment and therapy when such things are not only unnecessary but absurd and can even be harmful - especially in the longrun. It's reminiscent of various 'treatments' for homosexuality in the earlier years of psychology/psychiatry, which by the way does not mean t…
This post answers yours clearly: it is a spectrum.
> I think a reasonable definition would be a disorder
Homosexuality is not a disorder according to ICD or DSM. Autism is a development disorder. Schizophrenia is a psychotic disorder. Disorders cannot be cured, and cannot be treated either. One can learn to cope with them, but it cannot go away like a traditional disease. Its a verdict for life, so to say.
Someone with autism can have other issues, on top of their autism, e.g. ADHD or depression however autism is the main issue from which the other issues derive from.
The rest of your post is just denial, and I can only speculate why.
> The definition of mental illness should not slide so far as to begin to encompass people that clearly are not ill by any meaningful definition of the word.
That's why we have specialists who analyse people, and not laymen like people themselves, or people like you who claim about random strangers they "they don't have autism" or "don't have severe enough autism". Those people who get a diagnosis by said specialists who specialised in ASD generally don't get misdiagnosed. You may safely assume that those people have ASD. If they're not a child anymore, that generally means they have a relatively mild form but as you can read throughout this thread that doesn't mean they don't suffer, or that there's no room for QoL improvements. You can figure out how adults with so-called mild autism suffer by reading into their stories. The linked story is a great anecdote though unfortunately the subject didn't get a diagnosis.
I am lucky enough to live in a relatively rich country with decent healthcare. But many in our world, including in the USA, are not as good off as I am. Those people might run around un(der)diagnosed. That saddens me, as I've been misdiagnosed and un(de)rdiagnosed myself for a good 3,5 decades.