Man was not meant to know...

[seawasp]

Question-boosting for James Nicoll, because I find his question very interesting:

Where does "we cannot tell the public about (something) because it would
trigger mass panic", where 'something' = something that either affected
the public profoundly or could affect the public profoundly, come from?
Not the "An Enemy of the People" variation, where it's just people
covering their ass at public expense, but where it's sympathetic
protagonists choosing to keep vital, need to know information from the
public?

It's a good question, and a meme that's essentially universally known -- to the point that I often have heard people using this meme as fact ("the government wouldn't tell us about aliens landing because it would cause a panic!"). But I admit that while (as others have already mentioned) there are similar comments in various stories like those of HPL back to the 30s, I have no idea where it originally came from, or if it has ever really been used in a real-world context.