Under one view, it is worse to torture someone than to kill him, at least provided the level of torture is sufficiently high. That can hold, a’la Amartya Sen, even if the person, in the Paretian sense, would prefer to be tortured than to be killed.
Most of us, including left-wing opponents of torture, think it is OK to kill al Qaeda operatives to stop an operation in progress or perhaps even kill them pre-emptively with reasonable cause. Those same people don’t think it is OK to torture, except under extreme circumstances. They also usually think that the slow torture of jail, including the homosexual rapes, is OK or perhaps to be ignored rather than to be either endorsed or countered (read Jane Galt on related questions).
One question is why (traditional) torture should be so much worse than murder. For instance we might think that torture is worse for "public choice" reasons. Perhaps the "mentality of the torturer" infects the body politic more than the "mentality of the murderer." Perhaps it is more likely that torture privileges will be abused than that murder privileges will be abused. Well, maybe, but I haven’t seen the evidence. At the very least our current state of knowledge on these questions does not justify the extreme aversions of the anti-torture critics.
(Could it be that torturers are simply less admirable than murderers, as Robin Hanson suggested to me, and thus we like torture less?)
I toy with the moral view that torture is simply worse than painless murder. Pain is a bad in a way that a missing life is not, noting that we must make adjustments for the pain of the relatives of the murdered. Forget about comparing just the consequences of each action, there is something relational and enduring about the torture which is highly objectionable.
But no matter where I come out on that issue, I endorse a strong anti-torture view because I am in general anti-punishment. Punishment is sometimes necessary, but in my core I think it is also wrong to send people to jail and that we should do so only with great trepidation. Of course this view is unacceptable to the American public.
Many torture critics, willingly or not, end up with a waffling view on the sanctity of life. In their moral schema murder is less bad than torture. Sure, murder can still be "very very bad," but surely we start to wonder why lives are worth less than avoiding pains. Some extreme pacifists will argue that we have no license to kill the same operatives we might otherwise be torturing. That position would at least be consistent.
I believe the anti-torture forces, of which I count myself a member, find it easy to posture on the torture question, but overall they do not sit in an easily defensible , or for that matter popular, moral position.
Last week Robin Hanson dared me to write a pro-torture post; this is the closest I can come to that.
Addendum: International law, and other legal documents, surely creates other differences between torture and murder, but I am asking the prior question of how those laws should read.