This point, "my surprise is consistent with the fact that people poorly understand each other, all too often" reminds me of a quote that was attributed to Kurt Gödel. He reportedly said,

“The more I think about language, the more it amazes me that people ever understand each other at all.”

And Gödel ties into conspiracy theories, too. I seem to recall that he died by starving himself to death because he thought that people were trying to poison his food.

On this point, "Regarding conspiracy, it's just a fact of life that conspiracies happen", Michael Shermer made the same point in the constructive conspiracism post.

If I remember correctly from the November post, he made a truth table style of argument, saying that believing in a false conspiracy theory is usually harmless, but believing in a true one is helpful, so even though false theories may be more common than true ones, it's still evolutionarily beneficial for people to have a predisposition towards believing them.