Just to make sure, are you advocating a concept of property rights from force? If I have the weaponry to steal a piece of land from another, I therefore own it? Historically this is how it has worked -- in many years -- but that doesn't validate the core concept.
What would be the non-utilitarian proof of the Right of Conquest. That is, the philosophical proof and not the practical implementation of it.
I personally think it's a weird set of morals. It resembles ethical egoism.
Example: if I have the power to conquest and enslave a person, would that be ethical?
Ethics are fictional concepts which only exist within a framework of laws. I'll call them laws of civilization.
Force operates outside of civilizing laws and all ownership of property requires the exercise of force to acquire and retain property absent any framework of civilizing laws.
Ethics describes moral values, which then differentiate good from evil -- right from wrong. Moral values, in most parts of the world (if not all,) also differentiate good force from evil force.
Libertarian ethics defines rightful property (i.e. exchange and homesteading) and force (i.e. non-aggression principle.) By force, with neglect to ethics, one can obtain resources, but this doesn't make it their property. If the obtained resources was another's property, the person who took them, stole them. Thus these resources are not the thief's property, but still the original owners'. If the stolen property is not returned, the practical outcome of the situation makes it look like the thief is the owner -- as he exercises exclusive control of it. But this, again, doesn't change the principle.
Thus force doesn't operate outside of ethics, but is defined as either right or wrong, by it.
Words themselves have no meaning without the defining concepts behind them. And are the framework for ficticious laws. Fealty to the ficticious law creates the mechanism for the application of force. Good or bad is defined by who is the recipient of the pain involved from the application of force and will always be subjective.
Private property is the result of the force necessary for acquisition and retention. Law is Created to bind men into contracts of fealty to protect private property against an organized threat to that property.
Libertarianism pretending you're free while staring in the face of laws that present ownership over you; simply because you say force is illegitimate. It's actually more legitimate than ficticious laws. Force of the defacto law and nobility is swearing fealty to the ficticious laws that define and protect minority rights and not fealty to another person.