Unfortunately, poor Nat doesn't seem to be able to put his finger on the real reason.
Nat Hentoff is a true Constitutionalist and an original “Liberal” in the classical sense, not the Marxist sense that is so prevalent nowadays. I had the pleasure of meeting him once on the street and told him that while I didn’t always agree with him, I respected his opinions and his defense of the Constitution and he replied with a big smile: “That’s what it’s all about!”
He may not believe in original intent but he’s far from being a Leftist Kook.