The way you describe anti-vaxxers sounds just like the climate-science deniers I’ve been studying — but interestingly, while climate science deniers tend to be conservatives, anti-vaxxers have a reputation for being liberal (though the actual data suggest that it’s nonpartisan and “the more political someone is, the more likely he or she is to believe that vaccines are unsafe.”) The arguments and resistence to evidence are also reminiscent of anti-nuclear-power activists, who tend to be liberals. I think, actually, that focusing on all these issues may have made me less liberal and more cynical over time, just because I know that highly political people also tend to be unreasonably biased — and often downright mean.

This article suggests a common thread, conspiracy theories: “endorsement of a cluster of conspiracy theories (e.g., that the Federal Bureau of Investigation killed Martin Luther King, Jr.) predicted rejection of climate science as well as other scientific findings.”

But not all of the people who are rabidly anti-vax, anti-climate-science, anti-evolution, etc* are into conspiracy theories. So I think another big factor is something that affects all of us: confirmation bias. We change our minds less often than we think; too many of us massively favor information we received earlier, so that it takes an unreasonably huge amount of evidence received afterward to change our minds.

Every human being has this flaw, and I think of all these anti-science people as one big cautionary tale. When you feel very sure you’re right about something, that doesn’t mean it’s true at all.

* Cue the people who say “oh I know climate science is right, it’s just vaxxination science that’s wrong” or “oh I know vaxxination is safe, it’s just evolution that’s nonsense” —guys, all these groups make the same kinds of mistakes. There is not something special about one particular kind of science that makes only those scientists wrong.

“It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.” — Josh Billings, 1874