It would be very instructive to go back in history and see how autistic people functioned and were viewed 500 or 1000 years ago. My guess would be, generally better than now.
Two of my own biggest ptoblems are 1) sensory overload--noises, bright lights, very crowded spaces, many people talking at once, amplified announcements, and 2) information overload--people talking as I'm simultaneously getting messages from several internet-based instant messaging sevices, plus ringing phones, plus email, plus the expectation to be able to multitask and do work as all this is happening, plus dealing with the previously mentioned sensory overload.
Now imagine me living in a time with no electrically amplified sounds, no beeping buses and honking cars and revving motorcycles, no bright, flashing lights, no phones and Internet and TV and radio, and usually no expectation to focus on more than one task at a time. I think someone like me would function much more "normally." I might seem a bit eccentric in social terms, but I'd be a lot closer to the norm than I am in our world.
The point being, it's a difference--unfortunately a difference that's ill-suited to many aspects of modern life. Rather like a pale-skinned person having to work outdoors in the tropics. But we don't call pale skin a disorder just because it's less suited to certain environments.
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"Donkeys live a long time. None of you has ever seen a dead donkey."