From a psychology perspective, here's what I find fascinating: each of us holds his or her positions to be the correct ones. We have to work actively to consider both that our opinion can be wrong and another's opinion can be right. Most folks don't bother. They know what they know and it's frankly easier to exist in the certainty that one is correct than it is to consider other angles and positions.
We woo fighters spend a considerable portion of our free time actively attempting to combat ignorance with scientific evidence to show why the other side is wrong. The other side is adamantly convinced that they are correct and we are the ones who are ignorant. Seriously. It astounds me, as I am sure it astounds y'all reading this (okay, not my buddies who are on the other side and reading it, they're still trying to figure out why we won't listen to parents's stories-- because stories are ANECDOTE not science and no way of guaranteeing the accuracy).
I offer as evidence the certainty of their convictions and the reason why in all likelihood there is a large proportion of those who devoutly hold their vaccines-are-the-root-of-all-evil (see Crosby's new article blaming AIDS on vaccines), this comment from a poster at AoA:
"Your description of the ignorance and disbelief we have to surmount to successfully warn and inform our "neighbors" about what is happening with vaccination in this country is exactly what I cannot seem to overcome, not even with family." http://www.ageofautism.com/2009/06/setting-the-scene-part-2-on-the-generation-rescue-fourteen-studies.html?cid=6a00d8357f3f2969e201157037d4c5970c#comment-6a00d8357f3f2969e201157037d4c5970c
Well, thank all that is holy that they encounter resistance.