We do so with the intention of protecting them from the dangers of the world. Undoubtedly, it is a laudable goal. The giant assumption we make is that we know better than they do, which is probably true up to some point in their lives. Of course, figuring out where that point falls is the riddle every parent faces. When we bring secrets into the adult arena, however, the situation gets a little more complicated.
Most people love a secret, that is, as long as they are in on it.
The reason, I think, has to do with the fact that secrets are fundamentally hierarchical. By its very definition a secret implies that someone knows the secret and someone else has been excluded from it. And implicit in any secret is the fact that an assessment or a judgment of character has been made. It is akin to being given a little dose of ego. There would be no point in being discriminating with information.