We DO need journalists. Quite true.
But as DanT says it is in the interests of those who sell us the news to make sure the said public is kept largely ignorant of pertinent facts and underlying issues on the basis that "it would be too complicated for them to understand" (or some other patrician bulls**t) in order to preclude the application of costly "journalism" rather than cheap sensationalism.
They bother because they have a job to do, pure and simple. Not perfect everyone agrees, but the alternative is a newspaper cover price no one is prepared to pay. In short, society gets the media it deserves - or at least is prepared to pay for.
Basically you are saying it's all right for a journalist to write a story which he knows is wrong or inaccurate on the basis that no-one will pay him enough to write the factual truth.
But if any of us took that attitude and it caused a plane crash, I can guess who the first people on the scene will be, shaking their heads in grave rebuke at the terrible negligence. But again, hypocrisy always has been the mass media's strongpoint.