Firstly, no, of course nobody here is required to argue for progressive causes. All points of view are welcome if they are made respectfully.

Second, I'll address the "implication that the Trump appointees are unqualified". Here I believe the author is referencing the federal judiciary, where the Trump administration has indeed appointed a number of judges who have been rated "unqualified" by the American Bar Association.

Thirdly, let's discuss "the obliviousness to the fact that it's the 'conservative' Justices who tend to vote according to their understanding of the Law". There have been plenty of decisions where the "liberal" justices have joined the "conservative" justices in a majority opinion (like the "gay wedding cake" decision). I don't know what the overall numbers are on this, but I would propose there is a tendency to perceive that the conservative justices are the more flexible ones because of the fact that there is a conservative majority, so that when a conservative "crosses sides" it is more likely to sway the decision and become a focus of attention. And I do know that there have been an overwhelming number of 5-4 splits in recent years (moreso than there have been historically) where the political leaning of each justice just happens to neatly align with their "understanding of the law".

Finally, as to "the general conclusion that, if the Court fails to produce the desired outcomes, *then* pack it -- essentially vitiating the claim that the Court should weigh in on politics from the outside, rather than replace the Legislature or adjudicate-to-order" - this is an unfair representation of the argument being made here. The author is saying that if courts *fail* to leave political matters to the political branches and attempt, as you say, to "replace the legislature or adjudicate to order", then liberals should consider "packing the courts". Your overly general notion of "desired outcomes" obfuscates the distinction between questions of potential judicial overreach and the results of the laws that they may or may not overturn. The Affordable Care Act was not the result of a Supreme Court "outcome" - it was the result of legislation passed by Congress, and the Supreme Court (appropriately, in my view) declined to overrule it, because there was nothing "unconstitutional" about it. It is perfectly legitimate for the left to want to restructure the courts if they are failing to show deference to legislatures when they should. Conservatives have spent generations attempting to do just that for the sake of eliminating Roe v. Wade - which may indeed have been an example of judicial overreach (and the author accounts for this by proposing a shift to focusing on state legislatures). Of course, each side is ulitimately motivated by their desired legislative outcomes, but that should not prevent us from trying to come to some sort of a general consensus about the appropriate scope of the courts' power, and working to ensure a federal judiciary that embodies this consensus.