For a Catholic, the fact that something is “intrinsically evil” ought to be enough to end the debate. Indeed, it should suffice as a granite and immovable rebuttal to this entire line of argument since nobody, Left or Right, has the right to even consider the notion, “Let us do evil that good may come.”
But the pains and penalties of sin (by which we mean “risking the everlasting fires of Hell and eternal damnation”) aren’t the only reasons no Catholic should support the use of torture. It is also worth noting that right here in this world, a culture’s adoption of torture—even the “non-lethal” variety, and even in times of emergency—is a formula for social catastrophe.
For it—like legal abortion—is a slippery slope leading to, among other things, the creation of a special class of people who truly enjoy this sort of work and are good at it. Reward such work and create a special department in the government for it, and people like that tend to find ways to continue plying their special skills, even when they’re no longer wanted by the state that once supported them. Just ask the victims of the quasi-mafia, quasi-KGB operatives who are doing very well in the post-Soviet era of gangsterism in Russia.