"The case against 'harsh interrogation techniques' is easy if they don't work."

Corporate lawprof Gordon Smith applies the same observation to arguments about corporate social responsibility:

Naive commentators often attempt to win points by portraying corporate managers as unenlightened and backward. If they would just act responsibly, the argument often goes, the world would be a better place and corporations would be more profitable to boot!...

The tough issue isn't whether managers should be "responsible" when responsibility pays, but whether managers should forfeit profits to pursue a "responsible" path. Tellingly, corporate law doesn't have much to say on that issue. Legislatures ban many forms of irresponsible behavior, but the marginal cases -- the morally complex cases -- are left to managerial discretion.

Of course, it's great for your argument if you can show that what you think is the moral path is also something that is better for all sorts of selfish reasons (or even if you can just get people to believe that it is). But idealists should want to accept the challenge to show why their position should be taken even if selfish interests point in the other direction. It makes your moral argument stronger if you can get people to believe it even when it requires sacrifice. On the other hand, moralists should think about the consequences of their hardline positions. It's not all about making the strongest argument for what you already believe. You might be wrong, and your imperviousness to real-world effects can be dangerous.

(The terrorists themselves seem to have a hardline moral position that is impervious to real-world effects.)