My title is intended to provoke. Surely all decent people want politicians to behave in an ethical manner—not to lie, cheat, or steal. What I have in mind, however, is the tendency of contemporary academic writers on political theory, ethics, and jurisprudence to suppose, in the words of the renowned liberal thinker Isaiah Berlin, “that political theory is a branch of moral philosophy, which starts from the discovery, or application, of moral notions in the sphere of political relations.”…