written law is what separates decent government from totalitarianism. the idea that ones leaders will only punish law violators in a previously stated way is what separates someone like an American president (ignoring the patriot act) from Hitler and Stalin. it gives a general member of society a respect for rules and regulations as a deterrent from crime, not overwhelming fear of their tyrant. this goes back to the Babylonian king Hammurabi. and though his eye-for-an-eye system is not necessarily humanely modern standards, the concept has been emulated by every non Nazi/commy/tyrannical government since.