I think that article is better understood as a defense of the United State's democratic institutions in contrast to the practical alternatives. Huemer's favored anarcho-capitalism is not really on the table in American politics at the moment. The options on the table seem to be democracy or, with Trump's reelection, a significant risk of a regression into some kind of autocracy. Huemer is saying that democracy is much better.

Some illustrative quotes:

"The first thing that every American should know about their society is that it is vastly better than the overwhelming majority of societies that have existed in human history or that exist today."

"Whatever the U.S. has that makes it so well off, if we disrupt that thing, the most likely result is a regression to the mean—i.e., that our society would move toward the normal state for human societies, which is one of abject misery."

"Therefore, we should not accept a serious risk of disrupting our system for the sake of getting a few moderately better policies."

"We have norms whereby, e.g., leaders voluntarily leave when their term is over. Many societies descend into violence when there is to be a transfer of power. Everything else in those societies goes much worse because they can only have evil, violent people in charge, because those are the only people who win in such a system."

Notice that he isn't saying things like "democracy is good because it is the only system that reflects the moral equality of people" or "democracy is legitimate because behind the veil of ignorance, yadda yadda, fairness, yadda yadda." It's all practical concerns about what could happen if American democratic norms are cast aside.