For what it's worth, I don't think there is such a thing as over-sensitivity on this issue. Here in Australia, there is an organisation called the Australian Vaccination Network, who attempt to convince parents not to vaccinate their children (due to unfounded fears of autism, mercury poisoning, and even wilder 'Big Pharma' conspiracies).

Children who are too young to be immunised against pertussis (whooping cough) rely on all transmission vectors (ie people they come into contact with) being immune: herd immunity is the term, I think. Pertussis isn't dangerous for a more developed human being, but babies can die of it. One did - warning, sad. So yeah, that justifies loathing.

(Thankfully, the AVN has been all but disbanded thanks to the efforts of skeptic groups)