I think it's motivated a lot by fear of autism, which contributes the vindictiveness. It also seems to be an offshoot of the anti-science left, which embraces natural food, loathes agribusiness, and prefers alternative medicine to the hated big pharma. I think it's grounded in Romanticism [1]. There's definitely a mistrust of doctors, but I don't see it as being generically about control.

[1] http://en.wikipedia.org/wiki/Romanticism