modern psychiatry be like

Surprising amount of overlap, there

The leading theory for the cause is (and bear in mind I'm simplifying a heckton here) "we don't know". There's possibly a genetic component involved, but if so, then it's super complex and doesn't have a clear causal mechanism (in that a person could have most/all of the genes of interest for autism, and not be autistic, and we don't really know why that is. Or why some people have none of those markers, but still have autism). Environmental contamination is a possibility, but we don't know nearly enough to guess what that would be, given that it wouldn't necessarily be microplastics

But there definitely is a lot of evidence supporting OP's claim, in that we are very confident that our increased understanding of autism has led to an increase in diagnoses (especially amongst groups such as girls; I am one of those girls who only got a diagnosis because of our shifts in understanding). We are extremely confident that our rate of false negatives has dropped over the years (i.e. people who actually do have autism but go undiagnosed). However, it's hard to estimate whether the actual underlying true rate of autism has actually gone up, given how much our understanding has changed in a relatively short span

That is an odd leading theory.

Afaik the leading theory is people are born with it, and "it" can show in a lot of different ways, but a list of symptoms are very telling and there are clear patterns of behavior associated with it. Also there's a specific age when people start to notice autism in children most prominently.

From what I can tell, you can't "become" autistic.

And vaccines and autism only overlap because the age where autism tends to stick out in children falls bang in the middle of the age range where children get their vaccinations. So it lines up. But in a bunch of studies a direct correlation was never found, and neither was causation.

Autism used to be something that almost no one had ever heard about. ADD and ADHD were also in that category of things that no one had ever heard about.

When I was a kid in the 80's, people didn't have ADHD or autism. They were just weird or behaved poorly. The hyperactive kids would get scolded by teachers, who would send comments out to their parents to complain about how poorly behaved they were. Autistic children were called removed because they couldn't figure out how to fit in and behave "normal."

I don't think they're becoming more common, they're just diagnosed more frequently because there has been a lot more research on the topic and people are more aware of them

You didn't get this post.

People have been behaving "weirdly" since written history. There have been countless stories and reports about "special" or "weird" people. If you compare these hundreds of years old stories to the definition of Autism, there are a remarkable amount of similarities, almost impossible to be coincidence.

But these ancient people were never called autistic... Because the word for it was only invented in 1911. And until the 70s or 80s, no one really investigated Autism very much, only a few people.

People that lived in 1910 did not suddenly get Autism in 1911. They were already autistic, just finally someone categorized and invented a word for this set of behaviors.

So in other words, it's not suddenly autistic people appearing, it's that the people that previously just were "weird" are now being discovered as autistic. Like planets that were there before, but now are being discovered.