Marcus is right; the "Rotten Tomatoes" rating disparity between critics and viewers proves the movie's point; Andrew Breitbart was hated and is hated still. Yes, I'm guessing ideology has something to do with the 96% rating from viewers. But it's laughable to suggest that one extreme(high) has everything to do with bias and the other extreme(low) has nothing to do with bias. And Marcus is probably right that one, and perhaps more, critics never even watched the movie.
It's entirely believable to me that they were so smug and certain that the movie would reflect the caricature they hold of Breitbart that they didn't need to see it to know what was in it. Marcus is also right when he says the liberal media no longer has a monopoly but a stranglehold. The difference is important because grips, over time, can loosen.