Disclaimer: I have no quarrel with the mods using the term in the creation of this community. I understand why they chose it, as even if they share my disagreement with the term when applied to ADHD, there’s not really a better inclusive term. “Mental illness” is really the only other option, and naming a community that would probably invite darker discussions that the mods might not be prepared to handle.
Another disclaimer: I think the term is perfectly valid when applied to autism, as autism is not, to the best of my knowledge, a mental illness so much as a difference in processing. Being autistic is only “bad” in the sense that our society discourages autistic traits. (Apologies if this is wrong; I’m neither autistic nor especially knowledgeable about autism.)
The term “neurodivergent” implies that there’s nothing wrong with you if you have ADHD–you’re just special and different. But my ADHD is an illness that requires treatment. A lot of people will tell you that the only reason ADHDers struggle is because society is set up wrong, but I don’t think that’s true, at least for me. Being unable to remember anything, unable to self-start, and hypersensitive to rejection would be massive problems in any world. Sure, the world today is particularly brutal for ADHDers in a way we could probably mitigate if we reorganized society to be kinder, but that doesn’t mean ADHD isn’t ultimately a disorder that some people need to treat with medication and therapy.
The fact that cPTSD, and other mental illnesses, can cause many of the same problems as “from birth hardwired” neurodivergences, does make me tend to consider mentally ill folks as a type of neurodivergent too, personally. The difference is they might one day no longer have cPTSD, I guess, but one might as well say they’re neurodivergent now and might not be later.
Neurodivergent is one of those terms I find both very useful and very misleading, in that I don’t think “neurotypicals” really exist in the way people talk about them.
I think it’s best to think of it as an umbrella term much like queer, where it’s just an acknowledgement of the diversity of human life and helping others to understand that you may think, behave, and act a bit differently than most people.