Immigration- Some countries will deny you the ability to immigrate if you are diagnosed at autistic.

Courts- If you have to deal with the legal system, there is the potential for a diagnosis to be used against you.

Police- Police are notoriously ableist, and if they know you're autistic, it could put you in more danger than you'd be in otherwise.

Infantilization- The general public is very poorly informed about autism. Many people in the general public think of autistic people as being severely cognitively disabled. Even many people in medical professions, who would have access to your diagnosis information through your medical records, are very poorly informed and might treat you like a liar or as though you are incapable of making your own decisions.

Workplace discrimination- While you would not need to disclose that you are autistic at work, if your workplace found out, they could use that information to discriminate against you. Yes, it's illegal and unethical, but workplaces do illegal and unethical things all the time. Also, it's possible for workplaces to find legal ways to discriminate against people, and if they know about your diagnosis, they could try to discriminate against you for that. Also, if potential workplaces find out about your diagnosis through other means, like social media, they could use that information to decide not to hire you. Yes, that's illegal, but it's very difficult to prove.

To my knowledge there really aren't any downsides to a diagnosis, as a matter of fact you may even have new legal protections under the Americans with Disabilities Act, or ADA: https://autismsociety.org/wp-content/uploads/2021/11/ADA-Fact-Sheet-1-1.pdf

You also have a right to not disclose your diagnosis per HIPAA, so long as you wouldn't need an accomodation.

Immigrating to other countries can be much more difficult. Lots of countries will put you under a lot more scrutiny if you have any kind of official diagnosis, because it makes you seem less desirable when compared to another equally qualified applicant who isn’t diagnosed.

I wouldn't even know where to get a diagnosis as an adult. All the resources in my area seem offer evaluations to children only.

I just got assessed and am going through a divorce with a kid involved, AMA. Jk, uhhh I'm afraid my soon ex-wife will use it against me to get custody at some point.

It's expensive.

I've also seen a few people start to mold their personalities after a diagnosis. They'll start exhibiting stereotypical behaviors that they didn't exhibit before the diagnosis. It might be that they stopped masking, but it's something to be aware of.

Getting a diagnosis can be expensive

i would say the scrutiny of it -- i've never been diagnosed but i'm so weird in ways that match with the memes -- having to describe yourself in that sort of super pathologic language and formally 'label' it feels weird imo

I felt the same a year ago when I realized I might share some traits described by autistic people. It was first a relief, a convenient explanation to most things I struggle with, and some “strange” traits of mine.

However, a diagnosis is very difficult to get in my country (years of waiting, not even sure I would get it one day). I decided not to do it because I don’t feel it would change anything beyond the validation. I don’t consider myself as truly autistic since I have no diagnosis, but I keep it in mind when I encounter difficulties, and it helped me a few times.

I don't know about where you are, but here in australia, you don't need to take your driving test every year.

As for downsides, a dx precludes you from serving in the military, if that was what you were wanting to do.

A dx helped me a lot. I got answers for why i am the way i am. It also allowed me some room to move, in terms of allowing myself accomodations that other people don't need. Before i was dx'd i was really hard on myself. But now I've accepted that I am different and as such, i struggle with things that other people do not.

It should be noted i was diagnosed when i was 32, so quite late.

There are no real downsides to an official diagnosis. Actually, there are more upsides like getting job protections and even assistance through vocational rehabilitation and other community organizations.