[P]erhaps the truest teachers of moral philosophy are the outlaws and thieves who, as Locke says, keep faith and rules of justice with one another, but practise these as rules of convenience without which they cannot hold together, with no pretence of receiving them as innate laws of nature.
(J. L. Mackie, Ethics: Inventing Right and Wrong [Harmondsworth, UK: Penguin Books, 1977], 10-1)
