Putting The NAP In Its Proper Context
I contend that the non-aggression principle is not a contextless axoim and it requires a specific definition of the difference between genuine self-defense and the initiation of violence. There is a grave problem that thin libertarianism and plumb-line libertarianism runs into, which is that the non-aggression principle has to be properly specified and taken into its proper context relative to other more specific principles or values. Otherwise, one's conception of libertarianism may start to undermine itself by either assuming values that contradict the NAP or through vagueness in the definition of what constitutes the initiation of violence.
For example, I would contend that the value of revenge and the traditional concept of punishment inherently undermines and violates the NAP. I consider them to constitute justifications for ex-post-facto violence, which is a particular form of the initiation of violence. I would also contend that an absolutist view in favor of violence in defense of property rights undermines and violates the NAP because it justifies pre-emptive violence on the mere grounds that someone is on your property. So I think that genuine self-defense has to be clearly distinguished from pre-emptive and ex-post-facto violence, and the context for genuine self-defense is an actual threat to one's life.
The absolutist view, in contrast, is completely arbitrary because anyone at any time can just go "hey, you're on my property" and cap someone. But merely being on someone's property is an arbitrary reason to justify the initiation of force. You need more of a specific context than just "there is someone on my property". The "punishment" of being shot to death isn't even remotely proportional to the crime of trespassing or loitering. Compared to life vs. death, tresspassing and loitering is a fairly minor matter. It certainly does not merit arbitrarily shooting people unless the people truly do present an overt threat of force.
Furthermore, I reject the idea that being on someone else's property means you forfeit your right to life and liberty. It might mean that you have an incentive to generally cooperate, compromise and abstain from infringement, but not that you lose all of your rights all of a sudden. A theory of property rights that overtly undermines the right to life and liberty needs to be fixed, otherwise it is going to be hopelessly inconsistant, even sinking to the level of justifying what are clear cases of assault and murder. Clearly, a consistant theory of rights has to uphold all of the rights, not misdefine rights to the point where one's alleged defense of one right inherently violates another right in the overall network of rights-concepts.
While Objectivists may tend to have a more integrated social philosophy than thin libertarians, Objectivists also fail to put the NAP in it's proper context, since at least the Piekoff-influenced Objectivists openly justify pre-emptive violence on the largest scale possible in the form of the invasive military apparatus, and there is a degree to which Rand was wishy washy on questions of American imperialism and she definitely seemed to throw a bit of a bone to the political right on questions of foreign policy. The problem with this interpretation of the NAP is that it totally turns a blind eye to the mass-death of innocent bystanders in the crossfire of conflict between nation-states. Scruples over private military proposals aside, thin libertarians actually tend to be pretty good on these sort of questions.
Where thin libertarians tend to fail most, however, is in the realm of pre-emptive violence on a smaller scale, in the context of individual private property owners. It's at this point that thin libertarianism may carve a possible path towards vulgar libertarianism, with the baggage of advocacy of the alleged right of property owners to arbitrarily shoot alleged tresspassers and justifications for feudal or quasi-feudal landlordism. These kind of libertarians tend to treat property rights as axoimatic, and effectively they trump life and liberty in their framework. The tendency is to act as if property rights grants completely arbitrary or absolute decision-making power over other people who are on or make use of your property.
This is problematic because it creates tension with the more fundamental principles involved in individual sovereignty. The fact that I'm on someone's property or the fact that I may technically be capable of leaving someone's property does not mean that literally whatever they decide to do to me is inherently justified. The decision-making power that property rights grants a person should not be completely arbitrary, since it always must be put into the context of consistantly respecting other people's rights. Being on someone else's property should not imply that you are their defacto slave or no longer deserve to live, only that one probably has to compromise with the owner in order to make use of the property. Owning property should not logically grant someone completely absolute and unilaterial decision-making power over other people.
So if views on the NAP or the use of violence in general could be put on a spectrum or organized, I'd categorize it like this: (1) Pacifism - All violence is unjustified, including self-defense (2) Thick Libertarianism - The initiation of violence is unjustified, self-defense is justified when there is an actual threat to life (3) Thin Libertarianism - The initiation of violence is unjustified, except in defense of property rights, which is to be categorized as self-defense (4) Objectivism - The initiation of violence is unjustified, except when it is rational "retaliation" (I.E. ex-post-facto or pre-emptive violence is justified), which is to be categorized as self-defense. The problem with both elements of Objectivism and thin libertarianism is that they smuggle in initiations of force by miscategorizing them as self-defense. The thick libertarian option seems the most rational.