Most retweeters and Facebook reposters aren't informing, or even arguing. They are using headlines the way one might use a bumper sticker: to express who there are and bond with others.
From a user’s point of view, every share, like or comment is both an act of speech and an accretive piece of a public identity. Maybe some people want to be identified among their networks as news junkies, news curators or as some sort of objective and well-informed reader. Many more people simply want to share specific beliefs, to tell people what they think or, just as important, what they don’t. A newspaper-style story or a dry, matter-of-fact headline is adequate for this purpose. But even better is a headline, or meme, that skips straight to an ideological conclusion or rebuts an argument. (Source)