NEW YORK — Mark Zuckerberg’s abrupt declaration of a new “privacy vision” for social networking earlier this month was for many people a sort of Rorschach test. Looked at one way, the manifesto read as an apology of sorts for Facebook’s history of privacy transgressions, and suggested that the social network would de-emphasize its huge public social network in favor of private messaging between individuals and among small groups. Looked at it in one way, it turned Facebook into a kind of privacy champion by embracing encrypted messaging that’s shielded from prying eyes — including those of Facebook itself. Yet another reading suggested the whole thing was a public-relations exercise designed to lull its users while Facebook entrenches its competitive position in messaging and uses it to develop new sources of user data to feed its voracious advertising machine. As with many things Facebook, the truth lies somewhere in between.