It's worth reading it in full but this is a choice paragraph:
"The "most fundamental problem of politics ... is not the control of wickedness but the limitation of righteousness." The Nazis, the Jacobins, the ayatollahs, and the others who have made revolutions have all been self-righteous. Kissinger suggested that nothing is more dangerous than people convinced of their moral superiority, since they deny their political opponents that very attribute. Tyranny, a form of disorder posing as order, is the result. This was one of Edward Gibbon's arguments against early Christianity. Gibbon represented the Enlightenment in full flower, just as Metternich, Kissinger reminded us, represented its dying breath before the onset of modernism, with its righteous causes. In any event, Kissinger observed wryly, punishing the wicked is "a relatively easy matter, because it is a simple expression" of public decency, and thus not a crucial task of statesmanship."