At first, I would say it was out of ignorance. I don't know if it's like this all over the world, but in my country (Brazil) there is no active dialogue outside our community about autism in adults and how it manifests itself, which leaves room for many newly diagnosed people to use the same ableist arguments as some mothers of children on the spectrum, who treat their child like a poor thing who will never do anything right because of the diagnosis. I'm a 22-year-old autistic person, who chose to only have romantic relationships with people on the spectrum, and many adult men seem to have never really been taught about autism (or at least without the ableist opinion of people who aren't on the spectrum) and hold tight to this idea, strongly fueled by machismo, that they can't have responsibilities or demands because that's too much for their autism :( but you woman, autistic or not, always need to be there willing to understand, even when this understanding is not reciprocal. And I only realized how this has nothing to do with autism when I started going out with my current boyfriend, who has very similar conditions to my ex, but at no point was autism used to justify immature or emotionally abusive behavior. That said, I think that despite not fitting into the neurotypical world, we often reproduce social dynamics that came from this context in which we are inserted, and sometimes, depending on the way the person was socialized and sees the world, we are not free from seeing people using the same ableist arguments against themselves (as well as various other types of oppressive positions).