The phrase "cloaked in its mantle of objectivity" means that it purports to be objective but it is really not objective.
The phrase "a vision of the world easily consumed and digested" means that it is easier to look at pictures than it is to read text. It also means that people are quicker to draw conclusions from pictures.
The phrase "its legitimacy as an objective bearer of the news" means, in a sense, its right to call itself an objective bearer of the news. A "bearer of the news" is someone or something that brings the news to people.
perpetuates keeps (it) going.