I guess the last 5 generations of my fathers side of the family (and that goes back as far as rural Russia around 1870) having autism or autism-like bahviours makes me highly skeptical about most vaccine-related theories. Also i'm fairly involved with an online community for adults with autistic traits and disorders and for about 80% of us the idea that there should be a "cure" for how we are/act/think is pretty hard to take. Especially those with disorders like Aspergers, it's a bit much to be told there should be a way of preventing you being you. I know when DH and my dad read the linked page DH emailed back a long response about how computer modelling is a software field and not a medical science, and my dad said "let's go and cure some emotional people!".

I will admit, it can be a bit of a raw nerve for some.