In general, I think there is public awareness that mental illnesses exist as a concept, but very little knowledge is spread about the range of illnesses a person can suffer from. Every single person I have ever encountered in real life, except maybe one or two, has universally agreed that mental illness (no specification as to which one though) is always curable and manageable in some way, and think any argument against this is baseless nihilism or the bias of a "mentally ill person lacking in judgement". Even though places like this website are glaring evidence that this is not always the case. There is a huge refusal to acknowledge the poor quality of life for many people with untreatable illness.
I have not met a layperson, a clinician, or even future scientific researchers, who will admit or acknowledge that there are cases of mental illnesses which are incapable of being resolved with modern treatment methods. I know why people think this way, and there is more plausible deniability or justification for them to think this way, because they can't truly see the inner anguish or unhappy life another person is living day in and day out.
It's much easier to determine a prognosis if you physically see someone with a grim physical manifestation of something. Like, if you saw someone with severe gangrene, it would be a reasonable assumption that they are having a medical emergency and that dead tissue needs to be removed ASAP. People can see the level of suffering clearly with their own two eyes. When someone is experiencing extreme emotional pain day in and day out, it is very hard for the average person to "see" it and understand unless they have personal experience with this sort of thing themselves.
I think this is the rationale behind why MAID keeps getting blocked and is only available in very few countries. Gathering any information about treatment resistant mental illnesses is an elephant in the room not many people want to address, because it isn't really a "positive" narrative, even though this stubbornness is constantly setting back rights and progress for those who want things to change the most.
Awhile ago I saw a comment on the therapists subreddits, where many therapists were admitting that their colleagues didn't really believe in autonomy in general, not in regards to self-determination of mortality or anything like that, but they wanted to boss clients around about personal life choices they didn't like- not being religious, being religious, being openly gay or trans, quitting a job, not quitting a job... As long as people like this who want to micromanage everyone else and make decisions for them "for their own good" (AKA what they want, not the patient) are calling the shots in the medical sociolegal sphere, it is going to be difficult to have a more open discussion. These types of people think they know better than whatever the patients have to say in every single scenario, and few people push back on the bs.