Mr. Scalia's argument fails for several reasons.
Torture Does not Generate Useful Information
Initially, torture is a notoriously inaccurate way to obtain information. Indeed, it is well-known by professional interrogators that torture doesn't work. Experts on interrogation say that torture actually interferes with the ability to gather useful information.
So if torture is not an information-gathering technique, its only purpose must be punishment and/or intimidation.
Torturing People Who Can't Give Useful Information is Cruel and Unusual Punishment
Moreover, most of the people tortured in the "war on terror" were innocent farmers, villagers, who those against whom the neighbors who turned them in for a cash reward had a grudge against. And children were tortured.
Many of these people did not have any useful information. And since the U.S. military stressed quantity over quality (not actually demanding hard intelligence or probable cause to suspect that someone was a bad guy), this did not constitute a useful intelligence-gathering exercise, but simply horrific punishment.
Indeed, some of the people tortured as part of the "war on terror" were literally crazy, and no amount of interrogation or torture would generate any useful intelligence.
This was illustrated by an article in the Washington Post:
Retired FBI agent Daniel Coleman, who led an examination of documents after Abu Zubaida's capture in early 2002 and worked on the case, said the CIA's harsh tactics cast doubt on the credibility of Abu Zubaida's information.
"I don't have confidence in anything he says, because once you go down that road, everything you say is tainted," Coleman said, referring to the harsh measures. "He was talking before they did that to him, but they didn't believe him. The problem is they didn't realize he didn't know all that much."
***
"They said, 'You've got to be kidding me,' " said Coleman, recalling accounts from FBI employees who were there. " 'This guy's a Muslim. That's not going to win his confidence. Are you trying to get information out of him or just belittle him?'" Coleman helped lead the bureau's efforts against Osama bin Laden for a decade, ending in 2004.
Coleman goes on to say:
Abu Zubaida ... was a "safehouse keeper" with mental problems who claimed to know more about al-Qaeda and its inner workings than he really did.The article also says that Abu Zubaida might have been tortured for months.
***
Looking at other evidence, including a serious head injury that Abu Zubaida had suffered years earlier, Coleman and others at the FBI believed that he had severe mental problems that called his credibility into question. "They all knew he was crazy, and they knew he was always on the damn phone," Coleman said, referring to al-Qaeda operatives. "You think they're going to tell him anything?"
(Indeed, even prisoners who were not previously crazy ended up that way after being severely tortured.)
Sorry, Mr. Scalia. Torture is not a valid information-gathering technique. It is, in fact, the cruelest and most unusual punishment there is.
By the way, anyone, no matter how high and mighty, who helps create, promote, or justify policies that violate the Geneva Convention is guilty of violating the War Crimes Act of 1996. See this, this, this, this, and this.
So you have not only failed to justify torture, sir, you have also opened yourself up to very serious charges. And see this.