Libertarianism is an attempt to answer one question and one question only: When is the use of force justified? More specifically, libertarianism is about what the law should be (since the law is force) and about proportional punishment. Libertarianism says nothing on how people ought to act in every case. Libertarianism doesn’t even say that there is no scenario where it’s okay to initiate coercion. All libertarianism says is, “If you initiate coercion there are consequences for doing so.” People possess free will. Perhaps there are certain cases where people think it is better to do a small amount of harm in order to prevent a bigger amount of harm. Libertarianism does not say these people are wrong. All liberterianism says is what the law should be, not how people should act.
One common critique against the non-aggression principle is that there are certain situations where direct liberty ought to be violated in order to maximize overall liberty. For example, suppose it is possible to murder one person in order to save the entire world. Should a person do so? Libertarianism has nothing to say on the matter except, “A person has a right to life. All humans have the same rights. If you take someone’s life the victim’s heirs have every right to seek reparations and make you pay for what you have done.” So you have a choice: Kill one man to save the word and accept the punishment that comes with it, or don’t be punished and don’t kill the one man. The choice is yours.
When someone says, “let’s say it’s necessary to kill one person to save a million,” the appropriate response is, “Ok, why not you?” Barring that, let us grant this unlikely scenario for the sake of argument. A person decides to kill someone to save the planet. The libertarian question is not what you should do, but what should happen to you after you do it? There are a few possibilities. One is that the heirs agree it is justifiable to kill one man to save the world and so do not press charges against the murderer. Another possibility is that they do. The case goes to trial. The jury can either rule “not guilty” believing such a rare, unlikely scenario justifiable. Another possibility is that the jury says, “guilty,” and sentence the murderer to death. Now there are two responses that can happen. The murderer can either take his punishment and say, “I believe it is justified to kill one man to save the rest. I thought the world would appreciate the fact that I saved them, but it turns out I was wrong. Nevertheless I know I did the right thing and so am willing to take the punishment.” Another possibility is that the murderer can object to being punished and decry, “Yes, I think it is justified to kill one man to save the rest, but only so long as that one man is not me. If I happen to be the poor schmuck who is offered as a human sacrifice this is unacceptable.” If that is the case I fail to see the justice in the murderer’s actions.
In short, if there are cases where you feel it is in the interest of the many to violate the property rights of a few in order to maximize overall liberty, one possesses the free will to carry this out. But if they do so they ought to be willing to accept the punishment (which will be proportional) that comes with it. Otherwise they are all talk. Would I steal an apple in order to prevent myself from starving? Absolutely. Does the person I stole from have a right to get reimbursed even though I was starving? Absolutely. Should I be willing to take the punishment? Yes, since the punishment for stealing an apple would not be death. I should take the punishment since the punishment for stealing the apple is less severe than having to die of starvation. In such a case everyone wins. I get the apple, and the person I stole from gets reimbursed if he decides to press charges.