In HP, the world divided between wizards and muggles. Muggles supposedly have no idea that wizards exist and wizards are required not to reveal themselves to muggles. I don’t see, however, how the secret can be kept when so many muggles seem to know about them. There are several wizards from muggle families at Hogwarts, and in one of the books Hermione’s parents actually accompany her into Diagon Alley. And of course Harry’s aunt and uncle know.
So why does the Ministry of Magic bother with concealment?
IIRC, the Muggle government (ie. British Parliament) also knows about the existence of wizards. In the Prisoner of Azkaban (the third book), when Sirius Black escapes from the wizards prison (Azkaban), the Ministry of Magic tells the British government so that the general public can be warned about Sirius… however, they don’t tell people where he escaped from.
IMO, the Muggles aren’t told about the existence of wizards and magic in order to prevent panic and fear. Also, I think that magical folks tend to look down on the Muggles, and they think that keeping in them in the dark is for their own good.
Also, the books mention several times that even when directly confronted with magic, Muggles simply refuse to believe it. One good example is when wizards playing a joke make “shrinking keys” and give them to Muggles. However, it’s almost impossible for the Ministry of Magic to prosecute these people because the Muggles will “never admit” that the keys shrank and disappeared - they keep insisting that they must have lost them.
