Do not fear violence, my friend.

One girl told him bluntly: “My mother says that violence never settles anything.”

“So?” Mr. Dubois looked at her bleakly. “I’m sure the city fathers of Carthage would be glad to know that. Why doesn’t your mother tell them so? Or why don’t you?”They had tangled before—since you couldn’t flunk the course, it wasn’t necessary to keep Mr. Dubois buttered up. 

She said shrilly, “You’re making fun of me! Everybody knows that Carthage was destroyed!”

“You seemed to be unaware of it,” he said grimly. “Since you do know it, wouldn’t you say that violence had settled their destinies rather thoroughly? However, I was not making fun of you personally; I was heaping scorn on an inexcusably silly idea—a practice I shall always follow. Anyone who clings to the historically untrue—and thoroughly immoral—doctrine that ‘violence never settles anything’ I would advise to conjure up the ghosts of Napoleon Bonaparte and of the Duke of Wellington and let them debate it. The ghost of Hitler could referee, and the jury might well be the Dodo, the Great Auk, and the Passenger Pigeon. Violence, naked force, has settled more issues in history than has any other factor, and the contrary opinion is wishful thinking at its worst. Breeds that forget this basic truth have always paid for it with their lives and freedoms.”He sighed. “Another year, another class—and, for me, another failure. One can lead a child to knowledge but one cannot make him think.” Suddenly he pointed his stump at me. “You. What is the moral difference, if any, between the soldier and the civilian?

“The difference,” I answered carefully, “lies in the field of civic virtue. A soldier accepts personal responsibility for the safety of the body politic of which he is a member, defending it, if need be, with his life. The civilian does not.

Starshi Troopers, CH 2 - Robert A. Heinlein