I have blogged before about my skepticism of Judge’s relying on “common sense” (see here and here), specifically where judges as “experts” rely on their common sense. Eugene Volokh opines on “common sense” here:
I’ve always been skeptical of such praise of common sense, for two related reasons.
First, common sense often leads us to the wrong results. That’s especially evident in places where the rightness of the right result can be proven, such as mathematics, physics, astronomy, and so on. It often takes some pretty “fancy mental gymnastics” rather than “common sense” to solve problems in those fields.
And it’s also true in more practical fields, such as economics. I suspect that to many people it’s common sense that if you want the store shelves to always be filled, you need to have someone centrally planning production or distribution; the “invisible hand” can easily be dismissed as “fancy mental gymnastics” by those whose common sense inclines them against that explanation. Likewise, it was probably common sense to many that alcohol kills lots of people, directly and indirectly, and therefore banning it might be good — and it’s still common sense to many that guns kill lots of people, directly and indirectly, and therefore banning them might be good.
Second, even if your reaction to these matters is, “no, my common sense tells me that the free market is great, and this common sense is correct,” perhaps your common sense is in large measure molded by the “fancy mental gymnastics” of others — Adam Smith, Milton Friedman, and the like. And while your and my common sense may be well-tutored on these particular points, it’s likely that there are many other points, in the policy world and out of it, on which our common sense misleads us.