However, I think this could be replaced with the simpler: If you have met one person, you have met one person.
But that's exactly the point. The quote is pointing out that people with Asperger's or autism differ just as much as people without; the latter is commonly accepted and expected, the former less so.
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I think it was covered in the first sentence of the second paragraph:
“If you’ve met one person with Asperger's syndrome, then you’ve met one person with Asperger’s syndrome.”
However, I think this could be replaced with the simpler: If you have met one person, you have met one person.
But that's exactly the point. The quote is pointing out that people with Asperger's or autism differ just as much as people without; the latter is commonly accepted and expected, the former less so.