But those claims are precisely what makes Mankiw's class and textbooks biased: namely, the refusal to step out of the mainstream and look critically at what is being taught. Those who claim that Mankiw's approach is bias aren't simply saying that what is being said is too conservative and that it needs to be more liberal. The problem with Mankiw's approach lies in the limitations of the assumptions in the theory being discussed, methodological issues, and in the failure to recognize that there are alternative approaches to neoclassical economics. To refuse to do so is a refusal to provide his students with the education that they expect and deserve.
The purpose of a liberal education is to expose students to a plurality of ideas and modes of thought, and from the interview it seems like the Fox News anchor and Greg Mankiw would agree. But, Mankiw's supposed dedication to liberal education contradicts his approach to teaching economics. By teaching an exclusively mainstream approach to economics he fails to provide his students with a wide ranging and critical account of economics failing the students the education they were promised when they entered into academia.
It is not simply that he is failing to provide his students with the liberal education that they are promised, but that by doing so he is failing the broader project that is the development of economic thought. Throughout the history of economic thought most if not all advancement in theory came from people drawing from a plurality of ideas -- not by simply staying within the mainstream framework. By limiting the ideological scope of his class he is limiting the potential advancement of his field.