Let’s create a new national holiday to facilitate communication. It should be called “I Don’t Know Day.” Two purposes: To encourage people to say they don’t know something when they don’t know it, and B) Remind them that they look smarter when they admit that they don’t know something that they don’t know. We could also create a separate holiday called “Don’t Make Shit Up Day.”

Perhaps Macy’s could stage a parade for “Don’t Make Shit Up Day” to be held at the NYT, just constantly circling.
I support the notion: I’ve often felt that one of the best things that graduate school (physics) inculcated in me was the increased willingness to say ‘I don‘t know.’.
I must disagree with your second point: it would be better if people did look smarter to other people when they admitted that they don’t know, but I’m afraid that this is generally not the case, and self-assured lying about how much one knows generally looks smarter to most people than admission of ignorance. Again, I’m sad that this is so, but I’m pretty sure it is.