Economists don't claim that self-interest is a moral good. They simply recognize it's an important part of human nature, and that government and social institutions must be designed for the human beings that actually exist — callous self-interest and all.
Governments routinely bribe suspects into accusing others in exchange for reduced sentences. Thus, suspects are willing to say pretty much anything prosecutors want them to. Governments are fine with this.
While it’s easy to see how much we’re spending over there, it’s harder to see what we could be doing with all of those resources if we weren’t creating more problems abroad. We need to transform the way we think about our foreign policy and take Bastiat’s cue to try to “see the unseen.”