Antivaccinationists scare the hell out of me because people with no understanding of science will listen to their gibberish and believe it. I've had a negative view of pseudoscience for a long time, but it's only snice becoming a parent that I've really come to grips with the scope of the horrors that lurk among the scientific illiterati.
Our herd immunity is compromised when there are groups of unvaccinated individuals. Kids are now dying from measles and whooping cough because parents aren't vaccinating their kids. Antivaccinationists are scaring people into preventing their own children from getting sick, and many are dying from preventable illnesses.
Autism isn't caused by vaccines. This myth has been debunked in study after study. We've spent millions to combat an alleged connection that has never been shown to exist. Yet windbag celebrities like Jenny McCarthy and Jim Carrey, neither of whom has the slightest idea of how science works, go on national television and claim that there is a link between vaccines and autism. Whether or not they've got good intentions, they are wrong about the science and are endangering people's lives.
Peddlers of woo are not only scientific illiterates, but they are a danger to society.