Because Tabibi is intentionally confusing #1 and #2 in the examples in that link.
Fake news isn't a marketplace of ideas, it's the opposite. NPR is calling for roadblocks on fake news and misinformation. Many intellectual people who should better seem to intentionally promote the right to spread fake news and facts as something good for society because it is primarily helping their side politically. Whereas free speech is being able to speak your mind freely. We already have some limited laws restricting free speech like in cases of fraud and libel. Why shouldn't they be extended to news sources making up bullshit that never happened like NPR was suggesting?
Taibbi didn't cite any specific examples, so it's unclear how any examples could have been confused. He just wrote that a particular discussion program should have featured a wider range of opinions.
How are we to differentiate speaking one's mind freely from spreading misinformation? No human possesses perfect information.
Spreading third party misinformation is different from creating said misinformation. You could ask them where they got the misinformation and go up the chain till you find who knowingly made it up and don't have someone else to blame.
https://news.ycombinator.com/item?id=28426181