I don't how many times this argument has come up. No amount explaining things like:

• Andrew Wakefield's research was manipulated and fraudulent.
• The difference between correlation and causation
• That the rise in prevalence of autism might be due to
  broadening the diagnosis.

I have a background in biology/biotech, and it drove me crazy when friends would bring up autism/vaccines because of Jenny Mccarthy. They rather believe a celebrity than a friend with a degree biology! I'm glad now that most of them have come to their senses.