@Cuckoosheep I think you asked what people who don't want to split up diagnosis terms' reasons are. I can only answer for myself, but for me, a large part of the problem is the way the conversation keeps being brought.
I don't actually have an inherent issue with more specific diagnosis. My problem is that when it's being discussed, a lot of proponents of the splitting the diagnosis camp tend to do the same thing that they themselves are frustrated with; lumping everyone together under an umbrella. I think that for the most part, people on this thread have been more open to having a discussion that doesn't devolve into a shouting match, but even on here I've seen posters make assumptions about people who are not profoundly autistic that are ignorant, or downright rude. There are major variations in presentation, levels of difficulty and levels of independence amongst those who would traditionally have been diagnosed with Asperger's syndrome or HFA, but this isn't always acknowledged. Instead, there is a whole lot of shaming and accusations.
'You lot with careers and children and normal lives'
'You can't struggle that much because you are verbal'
'How could you possibly think that your difficulties are similar to my child who is doubly incontinent?!'
It's hard not to get defensive when you feel you are being attacked, and it can be really difficult to keep calm when feeling misunderstood. In addition, hearing those comments raise alarms for me. If people already think that people who are not profoundly autistic breeze through life as it is, what will that be like if we go back to separating the diagnosis? How will I be able to advocate for my needs, or the needs of my mum? Will she go back to being abused? Will we be homeless again? Will I be able to afford private care? Just like the parents and/or carers of profoundly autistic family members want the best for their loved ones, I want the best for mine.
As someone who doesn't fit in either the quirky professor or the 24/7 care group, I'm worried that an increased focus on A vs B will undo some of the recent efforts to highlight how varied the spectrum can be. That not everyone fits into a neat box, and that I might need more help than people expect, despite being verbal and of normal IQ. I'm fully aware that this sounds selfish, but similarly it sounds selfish to me that some who want the distinction have no issue with lumping everyone else together as needing minimal support in other to help their argument.
I'm not saying that you have done this btw and I appreciate being able to have a conversation about this. I personally feel not much in common with the ND movement; I couldn't care less whether someone uses autistic or has autism, I use both. I also in no way think that I am 'equally disabled' as someone needing 24/7 care. I understand that there are people who want to celebrate difference, but I have a disability that I'd rather not have, not a superpower. If a split in diagnosis can be done in a way that wouldn't negatively affect me or my family of course I'd be all for it, but the way some people interact on the matter doesn't give me hope that this is the case, so I'm worried.