Basic Economics Has a Liberal Bias

People to the left of econ 101 will typically invoke the phrase “political economy” to explain why, for example, econ 101 underrates labor unions. Conversely those to the right of econ 101 will instead invoke the phrase “public choice” to explain why, for example, econ 101 overrates utility regulation. But in both cases the critics are saying the same thing, namely that the moderately liberal policies advocated by introduction to economics textbooks are ignoring certain realities of institutional design, practical politics, power dynamics, etc.

That is 100% spot on. I just do not see how it fits in with his title. Maybe I am missing something but it reads like Yglesias is making the mistake of confusing economics with a morality play.