When people ask the question “can knowledge be detrimental”, I always think about how ironic that is. If knowledge really is detrimental, then even the knowledge of that is detrimental. It isn’t as simple as that, however. There is a saying: “ignorance is bliss”, and to an extent, that is true. For example, if someone is bad at keeping secrets, then they shouldn’t know something of a sensitive nature. The secret-keeper will feel burdened by the secret, and the secret-giver will be hurt if the secret is revealed. The secret might be for the benefit of a third party, who will also be hurt if the secret is revealed.
In the popular anime/manga series Attack on Titan, humanity lives within a walled city surrounded by man-eating giants known as Titans. The residents of the wall have been living there for a mere century, but believe that they have been there for much longer. Furthermore, they believe themselves to be the last of humanity and completely isolated. They don’t know, however, that they are merely on an island off the coast of Marley, a country who they (the island of Eldia) lost a war to 100 years ago. The king of Eldia modified the memories of the Eldians and marooned them on the island, completely isolating them from those who would seek to harm them. The king obviously thought that the knowledge of a world beyond the walls would be detrimental to the people of Eldia, so he shrouded his citizens in blissful ignorance.
Another example would be the series of novels written by Jeanne DuPrau; specifically, The City of Ember. Ember is a city located deep underground the Earth, hidden away and populated by people who were raised not knowing there is a world beyond the cave in which they dwell. The City of Ember was created by the Government as a contingency plan for human survival, in the event that the impending nuclear war would wipe out the rest of the population. The first generation of Emberites were instructed to raise their children to know nothing of the world above, so that they would not try to surface from their safe underground dwelling prematurely. Once again, the government officers in charge of the Ember project decided that knowledge would indeed be detrimental.
However, in both of these examples, there was a flaw in the plan. In Attack on Titan, the Marleyans sent undercover soldiers to destroy the walls of the city and let in the man-eating Titans. The Eldians were blindsided and massacred, not prepared for an attack and unaware of what to do. If they had known about Marley, they’d have been able to expect an attack and prepared. In The City of Ember, the time capsule (containing instructions on how to exit Ember and knowledge of the world above) set to automatically open well before the Ember supply stores ran out, was misplaced and not found for hundreds of years later. The lack of knowledge put the entire population of Ember at risk. The city was on the brink of electrical failure (which would plunge them into absolute, deadening darkness) and their food supply war running low. It was a fluke that the protagonists found the capsule and led the city out of the long-past-due-to-fail Ember.
In conclusion, knowledge can be detrimental, but one must consider the implications of ignorance too, which can be equally harmful.