The main argument in favor of treating it as a single condition tends to come from the advocacy side, rather than from the diagnostic side.

In terms of advocacy, there is strength in numbers, and arguably having such a large autism community has been good for both research and support. Potentially breaking that up into several smaller communities might lead to an overall decrease in impact.

On the other hand, pretty much everyone with autism, or families who have children with autism, will tell you that there is wide variation in both severity and presentation. And I think most would welcome better definition of subtypes.

I have serious doubts that an autistic advocate with low support needs, as opposed to 'neurotypicals' or impacted parents, are meaningfully more qualified to represent the needs of autistics with high support needs (e.g. severe intellectual disability, nonverbal, severe self injurious behaviors). Those autism are very very different with very very different lived experiences....and yet, well-meaning autistic advocates often bristle at that idea, almost as if it is an attempt to divide and and destroy autistic advocacy. The neurodiversity vs profound autism battle for hearts and minds continues to rage, and even threatens how and what autism research gets conducted...sometimes with good consequences, sometimes with poor consequences.

I am a proponent of finding neurobiological bases for subgrouping autism into different clinically meaningful etiologies so that the debate can move forward productively. Its one reason that more and more I'd rather forgo acquiring non-autistic controls in my studies, but just look within the autism sample for how to parse the heterogeneity into homogeneous subsets

I think “neurodivergence” is a better label if the goal is gaining strength in numbers. It fully encompasses autism and autism spectrum related conditions, plus ADHD and others. A lot of people don’t want the label “autistic,” but share experiences with people who do, and would love to offer solidarity as an “inside” rather than “outside” member of the community. We now have “AuDHD spectrum” as a thing, but really, I think optimum numbers might come from including folks who identify as “broadly neurodivergent.”

It also leaves room to start distinguishing/separating out more subtle variants of what we currently umbrella as “autism,” perhaps making it better defined in the future. And I kind of suspect doing this with “less profound” neurodivergencies could help folks with “more profound” (and rarer) cases.

To look at a historical case: Gay Rights didn’t make a lot of headway. But adding lesbians, trans folks, etc. ultimately did a lot of good for that community in the US.