The charge, as I understand it, is that Matt is guilty of demanding "abstract consistency" from normative theory. This, it turns out, is "totally wrong headed," because of a thousand words about Kant and Descartes and Fichte and Hegel and Habermas and Andy Clark and Joseph Heath and Rawls and Hayek which eventually get around to reminding us that norms are socially constructed, man. And society doesn't play by your rules, so if it turns out that there's some kind of abstract inconsistency in the normative arrangements it's made over the years there's really only one thing you can do:
This is an admittedly powerful argument! If we agree that our norms shouldn't be held to even the most minimal standards of abstract consistency, Matt's criticism is completely derailed.
The problem is that Hammond can't be content with the flight into radically antirational mysticism. He wants to save libertarianism from the rigors of consistency with a social construction argument, but he also wants to dignify libertarianism with the prestige of an "implicit rationale" that "can be rationally reconstructed". Yes, the "rationality of our social structures is...often hidden" - but we "ought to be able to extract and make explicit" their "implicit principles."
Have libertarians ever actually done this? I thought that's what they were getting at with their "non-aggression principle," for example - but then Hammond declared that criticizing the NAP's rationale was an inappropriate demand for "abstract consistency."
Needless to say, all of this talk about social construction is just a one-size-fits-all pretext for dismissing without argument any charge that libertarianism is inconsistent. Hammond spends about three-quarters of the article establishing the completely uncontroversial point that social construction is a thing; but where you would expect him to put in the actual work by demonstrating how social construction proves Matt Bruenig wrong, we just get vacous, leading speculation:
For example, perhaps “justice as fairness” isn’t a context-free normative standard which looms over all other practices. Instead, what if discrete norms like “I cut, you choose” or “lets flip a coin” or “first one to improve and enclose unclaimed land gets it” develop spontaneously through cultural evolution as low cost ways of securing agreeable cooperative social relationships?
ICYMI: Hammond spends about 600 words laying groundwork so that he can ask, "What if life isn't fair and homesteading is just the way things work?" I just got there in less than 400 words, and I had a wrestling gif.