That is: while ideally we would critically and deeply analyze every aspect of our life, we have limited time and energy. The reason we've been able to accomplish so much as a civilization is because we delegate thinking to others.
"Always doubt the media" is bad advice. It's similar to "always doubt your parents" because they told you Santa Claus was real. Always doubting the media is exhausting, and the author probably doesn't do it anyways, because he gets things done.
What's perhaps worth investigating is how technology can help us reduce the amount of trust we put in a single entity. The trend from news sites away from user-submitted comments is worrying, because that's an example of how one can read a story and immediately read critiques and reviews of it.
Quite ironically, Blake's platform of choice for this post (Medium) removed our ability to make inline comments on his writing, which is perhaps the best way to accomplish that.