So long as men desire to live together, no man may initiate the use of physical force against others.... When a man attempts to deal with me by force, I answer him by force. It is only as retaliation that force may be used and only against the man who starts its use. No, I do not share his evil or sink to his concept of morality: I merely grant him his choice, destruction, the only destruction he had the right to choose: his own.

For the New Intellectual: The Philosophy of Ayn Rand (50th Anniversary Edition) (ed. Penguin, 1963) - ISBN: 9781101137680