The danger of metaphor, as you well know, is generalization. People - and sheep - are more complex. Fully civilized people are not completely helpless...or dense. As another poster has noted, solid body language can dissuade predators.
The modern peacekeeping force takes on a multiplicity of jobs. They may be first responders in a disaster. They may negotiate with local leaders to stem terrorism.
Then there are the negotiators of the world. They are not sheep, sheepdogs, wolves, or pigs.
http://tedxtalks.ted.com/video/When-Should-We-Negotiate-with-T
I do agree that there are people in this world who take, burn, pillage with no thought to their victims. We do need a force to deal with them.