Like Kraftie said, we have the ability to hyperfocus but it's not the ONLY thing we do. In fact, seeing the "big picture," which would be the polar opposite of monotropism, is incredibly for anyone to be able to do whether they are Autistic or NT or anything else. I am wondering whom they think actually really, truly sees the "big picture" in anything? The only difference between us and them is that we have the ability to hyperfocus and they don't. So have decided to pathologize us for that. Now, granted, there are some Autistic who truly cannot see past their own noses and they are pathologized for it. But there are plenty of neurotypical people who do the exact same thing but they will never be pathologized for it. So it there legitimacy in monotropism? Sure there is. Is it exclusive to Autistic people, no. It might be more common with Autistic people but plenty of other people do it too.
The reason it's important to understand that we are not the only ones who do this, is that when it's seen in an Autistic person, the goal becomes to correct it. If it's seen in an nt they are just considered focused or obsessed and they are sent to therapy to correct it.
If you are an nt girl and you are obsessed with makeup and clothes, that is an acceptable obsession so that's fine. If you are an nt boy and you are obsessed with football and cars, that's acceptable so that is just fine. If you are an Autistic girl and you are obsessed with trains that is a pathological issue that needs to be corrected.
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"I'm bad and that's good. I'll never be good and that's not bad. There's no one I'd rather be than me."
Wreck It Ralph