The ‘wolves, sheep, and sheepdogs’ line did not originate in the film American Sniper, but showed up earlier, in a book by Lt. Col. David Grossman, On Combat; it was suggested by one of my military editors, jjmcdonald7911. Another similar quote is that ‘people sleep peacefully in their beds at night only because rough men stand ready to do violence on their behalf’, generally attributed to George Orwell, though his comments were a restatement of something said earlier by Rudyard Kipling, and only put in the final form years after Orwell’s death, by Richard Grenier. That quote I used in AFS, so I didn’t want to trot it out here.