In the Harry Potter series, Hagrid says that they need to keep their world secret to protect it from the outside world. He believes that if non-magic people (known as "Muggles") were to find out about the wizarding world, they would try to exploit its resources and secrets, potentially causing harm to both the wizarding and non-wizarding worlds. Hagrid also thinks that if the wizarding world were to be discovered, Muggles would fear and persecute wizards, leading to conflict and suffering.
Whether or not one agrees with Hagrid's belief depends on their perspective. From the perspective of the wizarding world, it may be seen as necessary to keep their world hidden in order to protect it from outside forces. On the other hand, some may argue that secrecy only serves to perpetuate fear and mistrust between the two worlds, and that open communication and cooperation could ultimately be more beneficial for both sides.