The grain of truth is that mainstream news doesn't live up to the standards they like to claim they do. The news typically gets the literal basic facts right, but they tend to distort and omit facts to fit their narrative. And opinion pieces are no better than blogs.
Where he stretches too far is his claim that because the mainstream news is biased, one can simply ignore it and believe whatever one wants. The mainstream news may distort and omit facts, but they do get the literal basic facts right, so if one's worldview contradicts the literal basic facts, then that person is wrong. And opinion pieces are no better than blogs, but no worse than blogs either; so if an opinion piece makes a valid argument, that's just as valid as an argument made by any other source.