“My little Johnny was a perfect student until the medical establishment gave him a learning disability!”
This seems to overlap psychologically with the “my child can do no wrong” crowd, the ones who blame teachers, coaches, librarians, video games, sugar, red dye, gluten, participation trophies, or pretty much anyone or anything except themselves for their child’s problems. The common thread is a profound lack of self-awareness.
On the anti-vaccination issue, there’s also a hefty dose of misinformation from people who are making money from selling the idea to gullible people, but there’s definitely a certain psychological profile who falls for it most often.