Scholars who want to explain things and also suggest reform find themselves in a difficult position. Suppose you have an excellent theory that can predict how justices will vote in Supreme Court cases. The theory's independent variables are all nonlegal factors, such as who appointed the justices, where they obtained their law degree, the region in which they grew up, etc. Next, the Supreme Court decides a case, exactly as predicted by your theory, but in a way that, you are sure, will greatly injure American society. You sit down to write an op-ed decrying this outrageous assault on the rule of law. "Put your pen down," says Jack, in effect. "Your own theory predicted this outcome, and your theory does not include, as an independent variable, op-eds written by outraged professors. Therefore, you are wasting your time (or just showing us that you don't believe your own theory)." See Jack's post here , which was a response to mine here , which was a response to his here , and see Dahlia's skeptical response to his initial argument.
This problem was called the "determinacy paradox" by a pair of economists — Brendan O'Flaherty and Jagdish Bhagwati — who realized that (for example) economists' efforts to persuade governments to lower trade barriers were inconsistent with economists' theories about why governments raise trade barriers. If trade policy reflects the influence of interest groups that care only about the welfare of their members, then it seems pointless to tell the government that free trade advances the public good. It's a powerful critique, and if Jack didn't also make normative arguments both on his blog and in his scholarship, I would be persuaded he believed it.
After all, Jack advises liberals and progressives (not sure which is the right word these days) to stop complaining about bad judicial reasoning and to start engaging in politics. Exercise your right to vote, engage in public criticism, join a social movement. If you succeed, you will eventually put into power presidents and senators who are willing to appoint Supreme Court justices who agree with your views. However, this theory, or at least one reading of this theory, does not escape the determinacy paradox, either. It only appears to do so because no one has a very good theory about how a social movement starts. But on one reading, Jack implicitly assumes an ironclad deterministic theory, one that says that social movements of one or another particular political coloring will come into existence when factors X, Y, and Z are present (say, economic disruption, large-scale immigration, the appearance of a charismatic figure, etc.). If his theory is a good theory, then whether or not you, the reader, engage in politics or join a social movement or do anything at all, future Supreme Court case outcomes have already been determined.
I don't think that the determinacy paradox is quite as troubling as Jack appears to think. Indeed, in another (probably better) reading of his theory, it makes sense to engage in politics, including the political activity of criticizing Supreme Court justices for too enthusiastically striking down statutes that contradict the political preferences of the party to which those justices belong. Let's agree that Supreme Court justices, today and in the future, are heavily influenced by "politics." And let politics include not just the expression of bare political preferences, but also arguments about publically beneficial institutional arrangements. Some people are cynical about institutional arguments, thinking that they are almost always disguised partisan arguments, but it is undeniable that, every once in a while, an institutional innovation benefits both sides of a partisan divide. Civil service reform, which limited destructive patronage battles between parties, might be an example. A more pertinent example would be the development of an independent judiciary. The argument today is about whether this judiciary performs adequately, or should be reformed. A strong case has been made that American Supreme Court justices have gone too far in evaluating and striking down laws on the basis of their constitutionality. In doing so, they contribute to a pattern of behavior that hurts Democrats when Republicans control the court, Republicans when Democrats control the court, and, the argument goes, everyone in the aggregate because the temporary gains for each side are less than the temporary losses and the permanent damage to democracy and the rule of law. The type of institutional deal that would be necessary to escape this cycle is no harder to imagine than other institutional deals that serve bipartisan interests. Existing Supreme Court justices might be led to see that in the long term, their personal, ideological, or partisan goals would be advanced through judicial restraint (because they benefit when the opposite party controls the court). Even if they don't, future Supreme Court justice appointers might. And the political branches, if they ever get tired of how the court behaves, might press for institutional reforms from the outside. The fact that most advanced liberal democracies have much less of this behavior makes this scenario quite imaginable.
This judicial restraint view might be wrong, but if so, it is wrong for empirical reasons that one would like to hear from Jack or anyone else. The response that Jack needs to give is not a discussion (however interesting) of how, historically, various political agents struggled for control and some of them adopted this particular view, in some cases for opportunistic reasons. You can't defeat a normative argument with a description of how others have made the same normative argument in an opportunistic fashion. Jack's determinacy-paradox argument, if taken literally, contradicts his own argument that people should engage in politics if they seek to improve the world. If taken in a less literal sense as a warning that it can be hard to persuade Supreme Court justices to change their behavior and that it's even harder to persuade others that particular institutional reforms will benefit people across the political spectrum, no one disagrees with him.