Outlandish theory: the anti-vaccine movement is caused by microorganisms directly controlling the minds of the humans they infect to maximize the microorganism's chances of survival and propagation. This mind control ability could be the result of evolution, not anything more sinister.
Inspired by Toxoplasma gondii reprogramming the behavior of rodents.
A further outlandish generalization is that microorganisms control a huge amount of seemingly "higher" human thought and behavior, so are the source of radical disagreements among people despite people being nearly genetically identical and living and growing up in nearly identical environments. There are also anecdotes of people radically changing their political beliefs as they get older: they've gotten infected, possibly due to a weakened immune system.
If these theories are true, should we reconsider "one person, one vote"? Free will?