They are perhaps impressively myopic, that they overestimate a statistically insignificant chance of an undesirable side effect of vaccination, while totally ignoring the significant chance of acquiring one of the diseases the vaccine will prevent, dying from it or having life long consequences as a result. But that is the mental health problem of anti-vaxx, is not looking at the big picture.
A widespread highly contagious fatal disease puts society at an even greater risk: panic. There's all kinds of examples of humans, even in relatively modern times, trying to eject sick people from society. And that's the kind version. Locking sick people in barns and churches, and burning them down, barricading burning entire villages to the ground due to fear of contagion.
You think the anti-vaxxers are terrorists? Not a good word anyway, but when the general population starts to freak out over a disease, that will be terror. The idea we're really that different from medieval times in the face of a virulent contagion is hilarious to me, especially with all the fantastic obsession with zombie shows.