A common problem libertarians are faced with is the application of the non-aggression principle in the case of human shields. Walter Block attempted to come up with a solution through his “negative homesteading” theory, with which I respectfully disagree. The problem is this: if A is aggressing against C while using B to shield himself from all defensive force from C, can C use force against B to stop A, and can B use force against C in order to stop C from using force against him? I posit that the libertarian approach is this: It is legitimate for C to use force against aggressor A, and if A aggresses against B to put B in a position to receive the force against him from C, than the one responsible for the harm done to B is A, that the one initiating force against B is A, not C, and that therefore B cannot legitimately use force against C because that would be aggression, as C is not initiating force against B, but simply having his defensive force blocked by A with an innocent person. As an example situation, imagine that someone attacks you by punching you, and you punch back, but as you are throwing your punch, he grabs a person next to him and places that person in front of him, causing this innocent person to receive the blow. Obviously (because your force was directed at the aggressor) you did not aggress against the innocent person, and, therefore should not be stopped from punching by the innocent, as that would be an initiation of force against you. The analysis is the same in a hostage situation in which the hostage is taken not at the last moment but well before, and one in which fatal force is used instead of a punch.
“Collateral damage” is still aggression because it is not a case of an aggressor using an innocent or innocents as a shield against defensive force, but aggression by a person in the course of using or attempting to use defensive force against an aggressor. For example, a store owner who has been robbed would be an aggressor, in fact a worse aggressor than the robber, if the robber ran into a crowd of people and the store owner sprayed machine gun fire into the crowd. This theory is not a justification for aggression against third parties when using force against an aggressor.
In conclusion, I hope this answer to a common objection will help people put an end to one of their doubts regarding libertarianism.