Autism Spectrum disorder is not a disability because for some this condition grants additional abilities, such as hyper-concentration or unique fashions of reasoning, where a disability by definition is the privation of an ability. ‘Dis’ is a latin prefix meaning apart, asunder or away . The word disability is the conjunction of the word ‘ability’ with this prefix. So, Autism can’t be a disability because it in fact adds abilities.
A practical example of this can be gleaned through a discussion of physical disabilities such as a lack of the ability to walk. A person confined to a wheel-chair is limited to that chair. Although they might spend more time reading because of this, that would not be an ability which went directly with their condition thus their inability to walk would be a disability. Does this situation make someone who must live with it less than human? Of course not. To state that someone is less than human because of a disability is fascistic because the Nazi regime in Germany murdered those with disabilities and fascism is all about creating a society which does not accommodate the weak.
However, a discussion of physical disabilities makes it clear that disabilities are distinct from the situation which is encountered by people on the Autistic spectrum (and people around them). This is further supported by the fact that Autism speaks states that people with this disorder have unique strengths. Autism could be better termed a parallel track of thinking therefore.