Another angle I'd like to explore is one alluded to in Banquo's Ghost's opening post:

I am aware that is not however, a universal opinion in a community where we have even had apologists for torture. I would be interested in those other opinions, and what safeguards might be proposed to prevent a plummet into the abyss.
Another thing that happens is "we" explain, or excuse or forgive ourselves (whom we believe to be civilized, compared to the barbarian threat). So an atrocity or some atrocities are commited upon "us" by "them" - who are beastly - and we explain to ourselves that we must shed our civilized selves and be atrociously beastly in return, promising that this is only temporary, because of the emergency, and for the sake of survival.

But, over a pretty short time, historically speaking, our own atrocities, temporary though we intend, also brutalize us ourselves, and gradually inure us to our own inhumanity.

Remember the shock and horror felt when the guy Danial Pearl was beheaded? Pretty awful, and only a few years ago. Now, though it's still gruesome, we've almost come to accept beheading as something that just happens. And it somehow gets twisted into a rationale to justify for example: waterboarding.

Indeed, the abyss gazes into us.