You are the President of the United States in the Buffyverse.

[The Romulan Republic]

Well, I think Buffy was just going along with what she had been taught to do, and never put a great deal of thought into it. Though she initially kept her role as Slayer secret to protect her family, as I recall.

But if you think it through... well, revealing the existence of all that stuff would cause global panic, chaos, and strife. Would it be worth it in the end? Maybe. But it wouldn't be a magic cure-all.

[The Romulan Republic]

This is why I would try for a "gradual exposure", I think. Much like what I've argued for in the past for the Harry Potter universe. Leak out tidbits, gradually ease people into acceptance of the supernatural, rather than having one big, sudden shock.

Although its pretty clear that a lot of people do know about the supernatural in the Buffyverse, at least in the later seasons. I recall in particular a reference to the LA DA's office using magic to defend against Wolfram and Hart in Angel's fifth season and a musician commenting that she hates playing in vampire towns or something to that effect in Buffy's seventh season.

And in the comics the supernatural is an open part of life. So the concealment did finally break down.