Insane people- or people regarded as insane, with conditions like autism for example- in primitive and subsistence communities often have a tendency of dying young, especially if there is a drought or some other disaster that brings about famine. People all over the world love and cares for their relatives no matter what, even if that relative is often regarded as a burden by others. However, dangerous individuals and those with severe disabilities often have fatal 'accidents' or 'disappear' one day. Sometimes it's because of blind prejudice, other times because the majority of the community think that the mentally deficient are cursed, and often because those who have periods of violence are too dangerous in a place where there is no medical aid and no resources to pacify them. Often they are outcast, beaten and chased away. And sometimes they are subject to brutal torture to 'cure' them of whatever demons are living in them. And sometimes, they're simply part of life for those around them.
OH&S, safety signs, free extensive education, concrete barriers, safety caps on chemical bottles, all of these are comparatively recent inventions. And before those were developed, many people died of 'accidents' that are entirely preventable today. You go back to when my own father was a child, he will freely tell you that by the time he left school, many of his friends had died. And while it was tragic, while they were mourned, death was regarded as part of life.
And, by an odd co-incidence, a large proportion of those who died were regarded as a burden were the ones who died young. When you have 5/6/7/8 + children to provide for, no matter how much you love your broken child, you have to weigh the cost of their care against the welfare of all your other children. And arsenic, by the way, was very easy to come by and the symptoms were very similar to many of the infectious diseases that ran rampart.
Diagnosis of autism continue to rise. And this is completely to be expected. The technology that allows identification of autism gets better and better everyday. The networking of families who care for their disabled relatives is amazing. No longer do they have to hide their flawed child or sibling away, regarded purely as a freak that can only be brought outside on a leash. They can talk amongst themselves, share information, support each other. Suddenly they are no longer judged by others for having a mentally disabled family member; they are judged for not taking care of their loved ones.
This network, however, works against itself; people who are autistic reach out to others who autistic, and find a partner who mutually understands. And given that there's a decent amount of evidence that many forms of autism are genetic... well, it's pretty obvious what comes next.
Look: I am on the spectrum and I had a brutal reaction to the measles vaccine when I was about seven, to the point where I'd probably have been better off if my parents had just sent me to an old fashioned measles party. I ran massive fevers and what do fevers give you? Brain damage. So yes, it is possible that I received some form of mild brain damage after receiving the vaccine. But the fact is, I was weird pretty much since I could walk, so if I did receive some brain damage from the fever, it really only added to something that was already there. And given that a fair amount of my father's close relatives born around the same time as he only avoided fatal accidents because they tended to have obscene levels of mathematical and engineering ability, autism absolutely runs on my father's side of the family. And so does bipolar, incidentally. We may not know the exact gene behind it, but it's definitely there. (For the record I got the 'tism but none of the maths. Not fucking fair.)
So yes, I do believe that, in cases where a bad reaction to a vaccine causes a severe fever in an individual, severe enough to result in brain damage, conditions like autism can either result or merely just be enhanced. I also believe that these cases are very, very, very rare, and often can be treated successfully anyway.
The fact is, at the end of the day, the rise of autism is a highly complex phenomenon. What isn't complex, however, are horrific and fatal diseases such as polio, whooping cough etc. If the drive to eradicate smallpox were conceived of today, it'd never, ever go ahead because anti vaccinators and SJWs would block the planes on the runway dribbling some inane bullshit about it being medically and ethically reprehensible, that vaccinating people in third world nations is a violation of their culture and rights, and that they are too uneducated to be able to make a real choice between accepting the vaccine or not. And yet, the program went ahead, and one of the deadliest, agonising and virulent diseases that killed millions of people over the course of human history is reduced to a small vial in a laboratory.
It comes down to this: are you more worried about hypothetical autism, or are you more worried about your child dying painfully from a preventable infectious disease and taking many others down with them? If your answer is the former, get the fuck out of the gene pool, it's there to swim in, not to piss in.