It is distrust of medicine as a science - look at what people are faced with:
- Doctors who wont prescribe birth controls, because of the doctors faith, not the patients.
- Anyone with the title "Dr" (of what, from where) can appear on TV and flog the latest magic beans from the amazon as a cure for everything, unopposed.
- Advertising for every 3 month cycle of trendy "natural/traditional/herbal/secret" cures also attacks pharmaceuticals as "unnatural chemicals"
- Any a time a doctor screws up its a news worthy event
- Everyone has a friend who went to a doctor (or doctors) that misdiagnosed something major (anecdotal: I know someone who saw 4 doctors before the last finally noticed the fist sized tumour growing a creeper up her spine).
- All doctors are paid by drug companies to play golf, everyone knows that.
Is it any wonder when something as scary as "MMR causes autism" hits the headlines, people take notice and don't ask their doctors. Everything in the media screams "don't trust doctors", why take the risk of autism, doctors have been wrong before?
As a parent of ASD diagnosed twins it certainly crossed my mind did it start when they were immunised. Certainly it was a traumatic time and I felt their behaviour changed after, but no, the symptoms were there before but they just were not advanced enough for it to be obvious. It didn't help that doctors kept telling us "they are twins, they will develop late" (see!). My wife and I as two reasonably intelligent people, knowing the MMR link was debunked, still wanted to put off further immunisations - the fear was there, even though we knew it was not to blame. How can you blame other people with less discerning processing and intelligence to make better decisions with so much bad information.
That said I really feel some parents want something to blame - "its not my genes, it was that evil MMR which was just a scam by doctors to sell drugs.". I looked for it when we got the news - something else was to blame, not us. I can imagine others do something similar.