America believes its right. The terrorists believe they are right. Using the logic that everything goes as long as you are on the "right" side quickly leads to more nastiness than we've already seen. The slippery slope that starts with torture lead to mass extermination of anyone you might suspect of helping the terrorists. And the line of "helping" gets pushed back a little further everyday. Suddenly, you are just rounding up and exterminating people because they might, possibly, have a connection to someone who might possibly have thought about perhaps attacking America.
Another way of thinking about it is that one of the central beliefs that Americans hold (as far as I’ve observed) is that the individual’s rights trumps the collectives (in almost all cases). This is pretty important as no-one wants their rights trampled for the good of everyone, unless the good that will be done is quite large and the cost to the individual is relatively low.