Michael Crichton explains the Gell-Mann Amnesia effect:
Briefly stated, the Gell-Mann Amnesia effect is as follows. You open the newspaper to an article on some subject you know well. In Murray's case, physics. In mine, show business. You read the article and see the journalist has absolutely no understanding of either the facts or the issues. Often, the article is so wrong it actually presents the story backward—reversing cause and effect. I call these the "wet streets cause rain" stories. Paper's full of them.
In any case, you read with exasperation or amusement the multiple errors in a story, and then turn the page to national or international affairs, and read as if the rest of the newspaper was somehow more accurate about Palestine than the baloney you just read. You turn the page, and forget what you know.
Something to keep in mind when you read the paper and the pundits and they're all telling you that of course we have to do X, and of course we should absolutely avoid Y, and of course there is no reason to worry about Z.
tl;dr - The mainstream media may lie sometimes, but mostly, they're just incompetent.