I agree that it would violate the NAP to damage someone’s stolen property in certain circumstances. Say, a thief steals your neighbor’s computer and is walking away with it, then running after the thief and smashing the computer would violate the NAP.

However, if the thief comes up to you and attacks you with the computer, then you can smash the computer in self defense, if that is necessary to protect yourself.

I also agree that if your only defensive action would violate the NAP, then you cannot defend yourself. The paper argues that this is not the case for the human body shield problem.

The author does make sure to mention that if we couldn’t damage the innocent person’s property, there would be some cases in which a criminal might be unstoppable…but he seems (to me at least) to be saying that this justifies damaging the innocent person’s property. If libertarianism is strict adherence to the NAP, then it is simply not the case that being in danger justifies violating the NAP by damaging an innocent person’s property. The author mentions that the right in the quilt would be invasive, but that does not mean that the quilt or the innocent owner of the quilt is violating the NAP – it just means the criminal is violating two people’s rights at once. Rights do not engage in aggression against other rights; only people can violate other people’s rights. In order to avoid violating the NAP, the person being shot at would have to attack the criminal on any part of their body that is not covered by an innocent person’s property.

He’s making a consequentialist argument, not an argument based on the NAP itself. While I’m inclined to agree with the author that it is legitimate to defend one’s self even if that means damaging someone’s property in the process(in those scenarios where a criminal is using someone else’s property without their consent), the only way for this to be considered libertarian would be if libertarianism is defined as those principles/actions/beliefs/whatever which are conducive to maximizing freedom rather than being defined as just, everywhere and always, strictly adhering to the NAP.

“An equivalent situation would be if the attacking criminal had
connected a device to your neighbor that would kill him if the criminal were
to die. If you defend yourself against the criminal, then your neighbor will
suffer. Yet, as in the p…revious case, your rights are antecedent to those of
your neighbor. The aggressor brought his property into conflict. The
violation of your neighbor’s property rights occurs when the criminal
connects the device to him, and when the criminal attacks you, not when you
kill the criminal.”

agreed – the violation of the neighbor’s property rights occurs when the criminal connects the device to the neighbor…but in the human body shield or quilt scenario, if you fire a gun at the criminal and hit the neighbor or their property instead, you would also be violating the NAP by violating the neighbor’s property rights.

“Furthermore, your neighbor would not be justified in
attacking you to try and prevent you from killing the criminal.”

As far as the NAP is concerned, i believe this is correct.

“One final case that should be examined is the following. Suppose a
vandal is about to mix your blue paint with your neighbor’s yellow paint, and
the only way you can stop him is to spill your neighbor’s paint. Your right to
determine if your neighbor’s paint is mixed with your paint is in conflict with
your neighbor’s right to determine if his paint is spilled. In this case, the
invasive action is the mixing of the two paints. The defensive action is the
spilling of your neighbor’s paint. Thus, you would be justified in spilling his
paint.”

Not really. If the only effective defensive action still violates the NAP, then it wouldn’t be legitimate under the NAP to engage in that action.