We kill each other, or threaten to kill each other, in part, I think, because we are afraid we might not ourselves know the truth, that someone with a different doctrine might have a closer approximation to the truth. Our history is in part a battle to the death of inadequate myths. If I can't convince you, I must kill you. That will change your mind. You are a threat to my version of the truth, especially the truth about who I am and what my nature is. The thought that I may have dedicated my life to a lie, that I might have accepted a conventional wisdom that no longer, if it ever did, corresponds to the external reality, that is a very painful realization. I will tend to resist it to the last. I will go to almost any lengths to prevent myself from seeing that the worldview that I have dedicated my life to is inadequate.
-Carl Sagan, from The Varieties of Scientific Experience