Self-Defense
"The necessary consequence of man’s right to life is his right to self-defense. In a civilized society, force may be used only in retaliation and only against those who initiate its use. All the reasons which make the initiation of physical force an evil, make the retaliatory use of physical force a moral imperative.
If some “pacifist” society renounced the retaliatory use of force, it would be left helplessly at the mercy of the first thug who decided to be immoral. Such a society would achieve the opposite of its intention: instead of abolishing evil, it would encourage and reward it..."
Read more about Self-Defense @: Ayn Rand Lexicon
Retaliatory Force
"The basic political principle of the Objectivist ethics is: no man may initiate the use of physical force against others. No man—or group or society or government—has the right to assume the role of a criminal and initiate the use of physical compulsion against any man. Men have the right to use physical force only in retaliation and only against those who initiate its use. The ethical principle involved is simple and clear-cut: it is the difference between murder and self-defense. A holdup man seeks to gain a value, wealth, by killing his victim; the victim does not grow richer by killing a holdup man. The principle is: no man may obtain any values from others by resorting to physical 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. He uses force to seize a value; I use it only to destroy destruction..."
