"Secrecy" is about just that - the modern history of nondisclosure in American intelligence, the public's need to know, the government's national interest in keeping its doings to itself. The documentary is framed as a debate, and directors Peter Galison and Robb Moss keep it divided almost evenly between fighters for the release of information (journalists, academics, etc.) and the intelligence folks who think that would compromise national security.
With the exception of an attorney or two, the participants are dug in firmly on their stances. The movie patiently cuts between them, but there's no rabid free-for-all. This is informed discourse, not ideological foaming at the mouth. It's a fair strategy, but it produces an answer I could have guessed before seeing the movie: Some secrets are bad (cover-ups, out-and-out lies). Other secrets might be necessary (for CIA field agents, say).