@clarencechampagne people claim otherwise because it's nice to imagine there's an inviolable inner sanctum of what you truly believe and who you truly are, and the notion that the core of your self can be changed not even from inside but by a bump on the head shakes people who emotionally rely on the notion of mental states being essential and transcendant, even when they're nominally a materialist. we like to think mind is safe from matter.
also coming from the political perspective people get very uncomfortable (understandably so) around the notion of people whose politics and conduct are cruel and harmful being that way because of a brain injury, stroke, illness, etc. some harm to them that they did not will. it breaks the notion of worldview and politics being powered by will and agency, which a lot of people, again, rely on for their moral political frameworks, even when they say they're materialist marxists.
To this view, If someone has harmful politics it means that they're a bad person. And if someone is a bad person, then they will that under their own agency. They chose to be a bad person and they could choose otherwise. The moral causation, under this view, arises solely from within the mind, rather than anything material. The notion that someone could become a harmful presence due to material situations outside of their control is deeply threatening to this sense of self, which is often taken for granted as common sense. The notion that we have ultimate and final control over ourselves, and the notion that we can keep our inner selves safe from the world by enforcing a determination on our own worldview, like, committing ideologically to a stance as protection from the world, is something that a lot of people, especially leftists, rely on, and the notion that you could get very badly hurt and come out of that with a brain that engages in harmful politics, engages in a harmful worldview, due to an injury, due to a disability, is morally threatening to a lot of people.
And I think that's understandable, but I don't think it's correct. I think there's a lot of compassion that's called for, regarding people who push back against the notion that, essentially, an injury, a disability, could make you what they see as a bad person. It's understandable why that would deeply freak you out and it's understandable why you wouldn't want to hear it. But I think the issue here is a deeper one of how people conceptualize ontology and ethics and morality and politics in general.
A lot of people see politics as about material, but they don't really fully grapple with the sense in which one's personal politics appear to arise from within the mind based on agency, but in fact are conditioned by material circumstances one experiences.