Ballon Juice makes this excellent point while discussing the controversy over a French TV show where ordinary people are induced to torture people to death. Some foolish people on Fox News and elsewhere are apparently under the impression that Americans would never do such a thing (despite ample evidence to the contrary).
It's pointed out that American story-telling in movies and TV likes to reduce everything to simple good vs evil story lines.
"The problem is that this attitude of good-self versus bad-other is not just a great opiate for those nagging feelings of doubt, it’s also an essential prerequisite for acts of incredible evil."
This is, of course, the point of the argument against torture, at the end of the day. We shouldn't torture people not merely because of what it does to them, but ultimately what it will do to us.
A similar dynamic was at work with slavery. Many contemporary and subsequent observers were of the opinion that slavery, while obviously detrimental to the slaves, was also detrimental to the slave owner over the long term. Indeed, I think one could make an argument that the persistent, nearly intractable social and economic laggardness of most of the Old South is a legacy of the "peculair institution."