In United States v. Eichman, for example, he voted to hold a federal statute forbidding the burning of the American flag unconstitutional, and it was certainly a vote against his ideological grain. But it is a curious example for a textual originalist to give. The relevant constitutional provision—“Congress shall make no law abridging ... the freedom of speech”—does not mention non-verbal forms of political protest, and Scalia and Garner insist that legal terms be given their original meaning lest the intent of the legislators or the constitution-makers be subverted by unforeseen linguistic changes. “In their full context,” they assert, “words mean what they conveyed to reasonable people at the time they were written—with the understanding that general terms may embrace later technological innovations.” That approach is inconsistent with interpreting “freedom of speech” to include freedom to burn flags, since the eighteenth-century concept of freedom of speech was much narrower than the modern concept, and burning cloth is not a modern technological innovation. According to William Blackstone, whom Scalia and Garner treat as an authority on American law at the time of the Constitution, freedom of speech forbids censorship in the sense of prohibiting speech in advance, but does not prohibit punishment after the fact of speech determined by a jury to be blasphemous, obscene, or seditious. And so an understanding of free speech that embraces flag burning is exceedingly unoriginalist. It is the product of freewheeling Supreme Court decisions within the last century.
I wanted to post all of that to give you an idea of what Posner is doing with his review of Scalia's book. But reading the intro to Posner's article, notice what Scalia is doing. He isn't claiming to be an "originalist", one who interprets the constitution based on the original intent of the founders. He's claiming to be a "textualist", one who interprets based strictly and purely on the text and the text alone. That's a sly attempt at a distinction. I think he's trying to make a distinction because there is no original intent. There were many founders and they had different views on these issues. I call it the "But, Hamilton" issue of constitutional interpretation.
What Scalia is trying to do by claiming he is a textualist is to avoid the "But, Hamilton" problem wherein an originalist points to a founder's opinion and someone responds with an opposing opinion from a different founder, thus nullifying the originalist's method of constitutional interpretation. Instead, Scalia claims to just point to the text, which on the surface is a safer method of interpretation. And even for a judge completely different than Scalia, an important part of interpretation.
But what Posner is showing is how difficult it is to adhere to the textualist method in practice. Judges are humans. They aren't a-political. We would like them to try to be. But I don't think it's realistic to completely remove any and all partisan leanings from their thought processes when ruling on a case. What we should expect is for them to make a good faith argument and be consistent with their logic. These are things Scalia has problems with. That and his tone are why liberals hold him in lesser regard than other conservative justices.
And just for fun, more from Posner:
Similarly, the book’s defense of the Heller decision fails to mention that most professional historians reject the historical analysis in Scalia’s opinion. Reading Law quotes approvingly Joseph Story’s analysis of preambles—“the preamble of a statute is a key to open the mind of the makers, as to the mischiefs, which are to be remedied, and the objects, which are to be accomplished by the provisions of the statute”—but fails to apply the analysis to the preamble of the Second Amendment, which reads: “A well regulated Militia being necessary to the security of a free State.” The preamble implies that the Second Amendment (which creates a right “to keep and bear arms”) is not about personal self-defense, but about forbidding the federal government to disarm state militias. Contra Story, Justice Scalia treated the preamble dismissively in his opinion in Heller.