Being wrong about aspects of reality is one thing. A bad thing, but only one thing.
The other thing, which sets these people apart from people who are merely wrong, is that they would rather have their children suffer the effects of lethal or crippling diseases than autism. That other thing isn't a thing that can be necessarily blamed on having bad information, or even on having a low intelligence.
The only thing outside of their control that can be used as an excuse for that is if they have bad information specifically about what autism entails. And that bad information in turn must specifically suggest that autism is worse than any of the relevant disease effects.
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I can make a statement true by placing it first in this signature.
"Everyone loves the dolphin. A bitter shark - emerging from it's cold depths - doesn't stand a chance." This is hyperbol.
"Run, Jump, Fall, Limp off, Try Harder."