Many libertarians claim that self-ownership is an axiom and is evident. I claim that self-possession is what is evident and that ownership doesn't exist as a property of anything (including people) but rather as a perspective (namely respect) of others.
Some claim that to argue against self-ownership is to fall into a performative contradiction because how can you argue against something unless you own yourself? Once again, I see such a claim as supporting self-possession or self-control rather than ownership. This, of course, ignores the fuzzy issue of what constitutes self, but I think that can be ignored for the purpose of the original claim.
So, let's put this performative contradiction to the test: if I kill you, does that mean that you don't own yourself? There's no performative contradiction there if action and control determine ownership. I took control of you (or at least away from you) then it stands that you yielded control and ownership to me. If the answer is "no" then there has to be something other than action and control that determine ownership.
If we stick with the original self-control yields self-ownership, what of the other animals? Couldn't a cow own itself because it has the will and ability to act in it's own interest just like a human? How can one justify owning other animals since those animals would own themselves and ownership (of self at least) is presumed to be exclusive?
Enter the appeals to human nature or our higher reasoning skills. This appears to me to be a case of moving the goalpost. Reverting to "humans are special internally" appeals may shore up the leaks in the philosophy temporarily but are terrible for an ethical system since ethics is about the interactions between actors rather than what goes on inside the black box of the actors' minds. To rely on the internals of the black box will be to rely on a god of the gaps, always retreating from the advancements of neuroscience as it reveals that humans are cobbled-together irrationality machines.
The leak can be eliminated and an ethic of liberty made consistent and pragmatic by adopting a paradigm of ownership-as-respect and recognizing that ascribing ownership as an intrinsic property of a thing is a mind projection fallacy. Such a recognition will require a similar shakeup in the conception of what rights are, and the boundary and nature of what rights can and ought to exist.