Was watching an older episode of the Nightly Show the other day and they were talking about anti vaxxers. Had a woman there from the Thinking Moms Revolution [1]. Larry asked her if someone came out with a vaccine against autism would she give that to her kids. She said she would not because she wouldn't trust it. So the problem is not autism but trust.
Another great insight from that show: this is about guilt and control. Something bad happens to your child => you feel guilty. You have the urge to do something about it, and while you cannot control lots of things, you can decide whether to vaccinate. This is similar to how people get eating disorders: food is often times the only thing they can control in their lives.
This was interesting to me because I cannot fathom how you can stare facts in the face and stubbornly disagree, putting your own child at a huge risk. This in no way excuses it, but it does highlight how someone goes from "I want my child to be well" to "I will not vaccinate".