Some information is classified legitimately; as with military hardware, secrecy sometimes really is in the national interest. Further, military, political, and intelligence communities tend to value secrecy for its own sake. It's a way of silencing critics and evading responsibility - for incompetence or worse. It generates an elite, a band of brothers in whom the national confidence can be reliably vested, unlike the great mass of citizenry on whose behalf the information is presumably made secret in the first place. With a few exceptions, secrecy is deeply incompatible with democracy and with science.