Many arguments can be advanced for and against torturing terrorist - some say it gets results and saves (our) lives while others hold that the information gained from torture is always suspect simple because of the methodology.
But there is an overriding point that obviates all these arguments for or against; simply that THE END NEVER JUSTIFIES THE MEANS (rather the means always shape the ends).
We are at war with whoever, because we are right and they are wrong. That's the basic premise in any democracy - we are there to preserve our moral way of life and if we use immoral methods to achieve this, we negate that premise.
Nothing else to be said - there is no argument, because if we behave like them, we become like them...