Unfortunately for us a condition that we don't really understand is far more prevalent than the side-effects of preventable diseases. I've never met anyone who's experienced post-polio syndrome or given birth to a child with congenital rubella. Alas I had measles myself, but I was too young to have been vaccinated.
This coupled with our odd perception of risk leads to people abandoning something that demonstrably saves lives because of the minor risk of side-effects. Having done some minor work with autistic children it's certainly not as bad or as certain as the documented outcomes of disease.
I don't think much will change people's minds until the diseases return, but I will be keeping up on the pro-vaccination side.