MetaHero "Justice without punishment is no justice at all."
I'm not entirely certain who you're quoting here, but I'd like to point out: at this point, Estaven has already been punished. He's dead. Most countries have outlawed the death penalty, but almost all have outlawed torture. In the US, people have lobbied for their executions to be postponed or altered based on the probability that the brief moments before they actually die will be extremely painful, and these petitions have met with occasional success. As Estaven himself points out, there's no practical reason to torture him at this point. He's being self-serving but he's not actually wrong, and Simon implicitly concedes that point.
If you want to get into the actual philosophy, most deontologists are going to say that Torture Is Wrong and stop there. Kant in particular would flip his lid—torturing Estaven in order to help Wendis realize her feelings is textbook "treating people as a means to an end." If you want something more contemporary, Shklar's whole thing is about how cruelty is the worst evil. You're not going to find many pro-torture philosophers these days, no matter what extenuating circumstances you get into.
Personally, if I were a different kind of consequentialist I might be more on board from the get-go. As it is, I'm still a kind of consequentialist and we don't actually know the consequences yet. And Simon's always been a means-to-an-end sort of guy—even if torturing Estaven ends up being the "optimal" decisions, I very much doubt he's going to try to argue that the act itself was a moral good.