The assertion of total power through unchecked violence - outside the Constitution, beyond the reach of the law (apart from legal memos from hired hacks instructed to retroactively redefine torture into 'legality') - will be seen in retrospect as the key defining theory of Bush conservatism. It ended with torture. Why? Because reality may differ from ideology; and when it does, it is vital to create reality to support ideology. And so torture creates reality by coercing "facts" from broken bodies and minds.
This is how torture is always a fantastic temptation for those in power, even if they first use it out of what they think is necessity or good intentions: it provides a way for them to coerce reality into the shape they desire. This is also why it is so uniquely dangerous. Because it creates a closed circle of untruth, which is then used to justify more torture, which generates more "truth." This is the Imaginationland some of us have been so concerned about.
The Western anathema on torture began as a way to ensure the survival of truth.
And that is the root of the West's entire legal and constitutional system. Remove a secure way to discover the truth - or create a system that can manufacture it or render it indistinguishable from lies - and the entire system unravels. That's why in the West suspects are innocent before being found guilty; and that's why in the West even those captured in wartime have long been accorded protection from forced confessions. Because it creates a world where truth is always the last priority and power is always the first.