Hmm, then we're all fucked. It's not just a matter of what one doesn't know but what one *doesn't know* one doesn't know -- the unk-unks ... unknown unknowns.
In any event, there's certainly much to be said for stupidity as a stress preventative. Being stupid means never having to say you're sorry. There are millions of Americans who quite sincerely believe the US is a force for good in the world because, bless 'em, they're incapable of perceiving evidence to the contrary. Being perceptive about the state of things is a form of torture -- it awakens you to all sorts of wrongdoings and gives you an incessant nagging sense of complicity in them.
Carl