Hannah Arendt, Reflections on Violence

Violence, being instrumental by nature, is rational to the extent that it is effective in reaching the end which must justify it. And since when we act we never know with any amount of certainty the eventual consequences of what we are doing, violence can remain rational only if it pursues short-term goals. . . .

The danger of the practice of violence, even if it moves consciously within a non-extremist framework of short-term goals, will always be that the means overwhelm the end. If goals are not achieved rapidly, the result will not merely be defeat but the introduction of the practice of violence into the whole body politic. Action is irreversible, and a return to the status quo in case of defeat is always unlikely. The practice of violence, like all action, changes the world, but the most probable change is a more violent world.

--From an essay in the New York Review, 1969