Because it's such an abhorrent and wrong action that if one had to justify it with some sort of twisted utilitarian logic one would need absolute certainty that it would save lives. Otherwise it would likely cost more than it would gain due to all the other inherent problems I have already said time and time again.
Besides, you will never have any chance of knowing a numerical probability that torturing someone will save lives. There is no realistic possibility that an Israeli interrogator will know that there is a 1 in 2 chance that torturing a detainee will save a life. That is impossible to know. It's a silly distinction that is designed to trap people into these useless hypothetical arguments that have no basis in reality. These kind of hypothetical arguments are not in any way shape or form useful in developing any kind of real-world legal framework so I see no point in continuing with them.
I was wary of giving some sort of moral absolute statement for this exact reason. As I said previously, such statements are useless.
OK again, the moral and practical side are, for me, related. Let's just get over this point because I disagree with how you're trying to form a moral foundation not based in reality.
I have already told you why torture is ineffective 3 times. 1) There is no guarantee--none whatsoever--that you will get useful information. The only motivation to tell the truth is to escape another round of torture. By that time it may either be too late or, theoretically, the detainee could continue to feed you BS forever while you continually follow false leads. 2) In a "war on terrorism," terrorists use knowledge of torture to recruit new terrorists. Case and point: the recording released yesterday by the American Al-Qaeda leader in Yemen summoning all American Muslims to wage jihad due to all the bad things we have done to Muslims, yada yada yada. These guys love torture and Gitmo. They eat it up. It's very useful to them in fomenting Muslim resentment and hatred of America. 3) Finally, what people seem to continually forget is by adopting torture out of fear of more terrorism, the terrorists have succeeded. They have terrorized us into adopting violent, inhumane, and offensive practices more befitting them than us.
Those few instances where we do get actionable intelligence out of torturing someone are not worth the risks or the erosion of our core values that lend us more legitimacy over the terrorists. We are different from them. We are civilized and we follow laws that are meant to uphold a fair and just society. We need to keep it that way otherwise we lose.
Humanity has devised a fully functional police and domestic investigatory system in the United States and elsewhere. Torture is not used in this system and yet we manage to find highly sophisticated and dangerous criminals all the time. We even *gasp* read these people Miranda rights!