Once that force is unleashed - and it is pure evil - it is almost impossible to stop it destroying your entire system of government. Maybe Europeans like me, who grew up in a land where torture was practiced by government widely in the distant past, and had that history dinned into us, understand this more acutely than those who have never known anything but a New World. But trust us Old Worlders passionate about the New: America and torture are mutually exclusive as ideas and realities. You can have one or the other. You cannot have both.
Like Sullivan I grew up in a land that practiced torture of all sorts routinely until it was forced to dismantle only 19 years ago. I was young when the regime changed but the stories of the government's practices basically defined my formative years, so I also have a pretty black-and-white view on the issue.
However, I think there is a greater problem, in addition to lack of perspective on the slippery slope nature of torture, and it's called 24 - the TV show - and what it stands for. Namely, since 9/11 the notion that torture under some circumstances is necessary has been widely popularized. Not surprisingly, I am not the first one to make a link between the two: see articles on the topic in the New Yorker and the Nation.