Critics of "torture" routinely complain that the popular warrant for "torture" is ends-justify-the-means reasoning. And they consider that morally indefensible.
One problem with their complaint is that, on the face of it, some ends do justify some means. That's not equivalent to saying any end justifies any means. Critics of "torture" are very slopping in that regard.
But now I'd like to make a different point.
(2) the terrorist has forfeited his right to life and his dignity by his own evil actions; and (3) the innocent lives that can be saved are of higher value than any moral claims by the terrorist who has committed atrocities.
While forgiveness and mercy are a matter for individuals, it is the role of the government to protect and punish. When it comes to protection, innocent lives that can be saved are of higher value than any moral claims by the terrorist who has and will commit atrocities. Guilt and innocence matters. If government officials have a known terrorist in custody, and it is certain that he has information needed to save lives, it is morally justified for them to use interrogative torture to get the information necessary to protect innocent life.
i) Notice that McAllister isn't using an end-justifies-the means argument here. Rather, she's distinguishing between lesser and greater values. In addition, she's distinguishing between prima facie rights and the forfeiture of prima facie rights. That's not equivalent to, or reducible to, an end-justifies-the means argument. Critics of "torture" will have to use attempt a different objection.
ii) It would be more accurate to speak of coercive interrogation rather than torture. Torture and coercion are not equivalent. "Torture" has connotations that have no relevance to interrogation.