I suspect part of your parent comment's point is that this is an implicit bias in the way the spectrum is defined and thought of, so it wouldn't be clinically defined in those terms explicitly.
In other words, the "spectrum" doesn't exist to capture the variation in the autistic person's own experience - if it did, it would look very different. It's a remnant of a time when autism was seen as just a "problem" for the people around you, and the spectrum measures how much of a problem you are and how weird you are seen by their measure; which does map onto a continuous line in the same way.
That does capture something useful, but only a small part of what autism actually comprises, and is much less useful at capturing the autistic person's own experience of it, and makes it a less useful tool to them than people might assume.
It's not unusual for diagnostic criteria to hinge on the impact the thing is having on your work/family/school life.
Alcoholism, for example - we don't define alcoholism as drinking ≥2 bottles of wine a week, or say that 1 glass of wine a week is part of an alcoholism spectrum.
Instead, we ask whether drinking often interferes with taking care of home and family; or leads to job/school troubles; or has lead to getting arrested.
How much of a problem an alcoholic is for others being roughly equal to how much of a problem alcoholism is for the alcoholic.
> Instead, we ask whether drinking often interferes with taking care of home and family; or leads to job/school troubles; or has lead to getting arrested.
We don't ask just that, and the diagnosis doesn't hinge on those - in fact those account for only 3 (or 4 depending on how you count) of the 11 diagnostic criteria for alcohol use disorder. The others are about the person's own experience with alcohol, the difficulties and psychological problems caused by it to the person themself. And that's for alcohol use, an external behaviour-based problem with a specific narrow scope. Autism is a much wider construct with much more varied impact and experiences, and yet in practice people are placed somewhere on the spectrum based mainly on external interactions and troubles.
Historically this came about because people who were "low-functioning" caused more difficulties to others, whereas "high-functioning" folk didn't - even though they might have comparable amounts of difficulties and psychological anguish internally and in need of similar help too. This simplistic view is changing slowly within the field and with some therapists recognizing it better for what it is, but it's still not nearly as widely recognized as it needs to be.
> It's a remnant of a time when autism was seen as just a "problem" for the people around you
I think it still is the current approach, and is not a bad thing per se:
People can have their own specific conditions, but if they are considered fully functional they will have no business getting clinically diagnosed. It will only be relevant when it reduces social functions, and becomes a problem, so that's the part that will be diagnosed.
To put another way, there is the biological/research part to understand how people work and how they think and behave, and the medical part to "fix" things. The variation of people's experience belongs in the former, the autism spectrum belongs to the latter.
Of course we do this for most conditions: for instance people's voice are all different, if yours is just "weird" but intelligible you won't go get a diagnostic, if half of the people can't understand what you say you might need one, whatever the biological cause is.
As someone who has "successfully" masked for the majority of their adult life, all the while suffering in silence, I can say that this is a problematic take at best.
I am considered a "fully functional" adult from all outward appearances, even to friends and family. I'm lucky enough to be capable (with great internal effort) of typical "normal" things like participating in meaningless smalltalk, holding down a job, and doing all of life's chores just like "everyone else." However, unlike everyone else, I had to practice and endlessly rehearse things in my head to achieve the outcomes I desired. A charitable interpretation of your words would mean that "it's a problem", but who is it a problem for? The folks around me? Certainly not. This is invisible to others. It's akin to running monte carlo simulations of all permutations of outcomes before acting on decisions that others would consider trivial. For years I thought that was what everyone was doing. I eventually learned that "no one" did this, and I trained away all "problematic" characteristics of myself just to keep up the act.
So in lieu of your implications that 'passing' autistics "have no business getting diagnosed", I'd rather propose this instead: seek a diagnosis if your condition is debilitating in any way shape or form and would benefit from treatment, _regardless_ of whether or not your condition is externally visible or even apparent to others. A "fix" should be sought if you are suffering. There is no cure for autism, but there are many programs and medications that can help.
PS That said, it may be unwise to disclose your diagnosis to say your employer, unless you need specific accomodations for your set of symptoms at work. I speak from experience.
I didn't mean to imply masking doesn't come with a disadvantage, and I sympathize with the efforts needed in places where others have no stress.
Still IMHO the bar to treat it as a medical condition is higher than that. To take another example, one can be hyper reactive to dust, and that has surprisingly wide impacts on everyday life. House maintenance becomes critical of course and interior furniture will reflect that (e.g. a long fur carpet and other hard to clean convoluted forms are out of question). It also bars the person from whole categories of shops ans places, old libraries is often a no go, some shops/restaurants using encent or heavier room flagrance will also trigger a reaction. There will be whole categories of jobs that are also not an option.
This kind of predicament will make everyday life a lot tougher and require significant effort, yet IME will not be categorized as a medical condition until something critical happens. Like an asthma crisis that ends at ER for instance.
It is not "fair" in the sense that successfuly dealing with the health/mental issue is kinda taken for granted, but I also understand why we draw a line between conditions the person can deal with alone, and other conditions that require external intervention.
I could "deal with it", until I couldn't. When a seemingly fully functional person with no warning signs suddenly breaks down (often catastrophically), providers scramble and tend to misdiagnose since they're missing key criteria. Without a formal diagnosis, it can look like severe depression or psychosis or a number of other similar conditions that have very different treatment plans. Autistic burnout treatment is something entirely different, although it can present the same. A prior diagnosis would at least point them in the correct direction for treatment.
In other words, the "spectrum" doesn't exist to capture the variation in the autistic person's own experience - if it did, it would look very different. It's a remnant of a time when autism was seen as just a "problem" for the people around you, and the spectrum measures how much of a problem you are and how weird you are seen by their measure; which does map onto a continuous line in the same way.
That does capture something useful, but only a small part of what autism actually comprises, and is much less useful at capturing the autistic person's own experience of it, and makes it a less useful tool to them than people might assume.