Perhaps it's because he characterizes people with autism as subhuman? And his attempts to do something about it are not grounded in evidence based treatment, but instead whatever foo-foo logic he's got in his head at the time.

If you told me, someone was looking into curing, say pancreatic cancer, I'd be happy, but if the same person was saying people suffering from pancreatic cancer are not fully human, and also that the cure is <insert disproven nonscientific cure>, not only would I no longer be happy, I'd be upset. The person is wasting valuable scientific funding that _could_ be going to funding a cure, and is instead denigrating people and redirecting attention.

Over time we got better at diagnosing it, that’s all. Mildly autistic people clearly existed in the past but were just considered odd or nerdy or something and now we can better diagnose and support those people