Note, again, that in his responses here, Dr. Gutzman is not saying “X is what should happen in a perfectly just world,” but rather “X is what ought to have been done if people were following the Constitution-as-written rather than doing-whatever-they-feel-is-best.” In the lectures both he and Dr. McClanahan have several criticisms of the Constitution that was drafted and ratified, and in their outside work no doubt they have more. But a course on Constitutional Law focuses on “what is Constitution,” not on “what is abstract justice in a philosophical sense” (though this later informs their critiques of the Constitution-as-drafted-and-ratified, that is, in the first several lectures). For that I recommend some of the many courses by Dr David Gordon at the Mises institute, and perhaps eventually Dr. Woods will present us with a course on political philosophy/ethics (which I for one would like to see). But this is distinct from that; that is not a book, and this is not a course, on “what a perfect constitution ought to be,” but rather a course on what was drafted, what was clearly understood to have been ratified, and the history of how that was perverted. Further this argument is to the effect that the Constitution should be altered outside of the legitimate amendment process – which is what constitutes arbitrariness and lawlessness, that is, factors unlikely to lead to justice – and we get what we have now, and it is an example of how that path does not lead to justice, but rather, destruction.
Beyond that, I’m going to limit myself to responding to one part of your post:
“But we do have an absolute duty not to commit any injustices ourselves, even if we have taken an oath to do so. This means, e.g., that a judge may never convict someone of drug possession, even if a law that is in accordance with the constitution obliges him to do so.”
It is also true that a person ought not take an oath they have no intent of fulfilling. Perhaps this means that as a consequence this means offices will be filled with less-than-fully-worthy people, but that is itself a consequentialist argument, and it is certainly true that if one takes an oath with false intent (I.E. taking an oath to uphold the laws, without mental reservation or purpose of evasion, but all along intending to not follow that oath because one disagrees with several of the laws one is swearing to uphold) insures that one is, oneself, a less-than-fully-worthy-person, is engaging in deception, and thus injustice.
Which is one of the grounds upon which some principled people state their opposition to getting involved in the political process, officeholding, and the like; that to do so is to commit oneself to some measure of injustice, and a breach of one’s integrity because one must either do what one thinks is right, or uphold your promise (the later of which – keeping one’s word and oaths – is certainly on the list of things a person of integrity ought to do. A person of integrity does not give one’s word/oath with the intention of breaking it).
I suppose it is a question whether an optimal constitution would empower a Supreme Court to serve as a body of Platonic Guardians, but the U.S. Constitution did not so empower them, so on that grounds I think Dr. Gutzman’s analysis is fair.