I think you are severely underestimating the mental gymnastics these people routinely go through to never be wrong about anything.

When you go to the doctor because you child is on the spectrum. "Fill out this form Mam", on it is the question "Did you take Tylenol during the pregnancy?"

- You check "Yes" -> Your fault, should have known better. No help for you.

- You check "No" -> Well then it can't be autism, that's "scientifically" proven. No help for you.