Exactly. I don't think anyone argues that there is no such thing as autism (or hyperactivity, or depression). There may even be more cases than in the past ... because there are more people, for one thing.
However, when you look at the literature on diagnosing "disabilities," it's clear that absolutely anyone can be diagnosed with a "problem" that has tax-funded "treatment." Out of my four sons, I have two I could easily get an "autism-spectrum" diagnosis for, and one ADHD. And these are perfectly functional kids. One needs a lot of exercise, and two are kind of peculiar.
When you define "disability" in a child as "any quality or behavior that an adult finds strange, tiresome, or inconvenient," then yeah, every child is disabled!
Don't you know that the government estimates that at least 50% of Americans have mental problems or will develop them ?
We're all nut jobs. ;)