Self-ownership

According to Charles Magney, Libertarianism

all stems from one first principle, "self ownership". Past that it is a big chain of reasoning from that first premise:

1. You own yourself. You have sole ethical jurisdiction over your body, and self determinism.
2. You owned yourself in the past, and you own yourself in the future.
3. If someone takes materials that you labored on in the past, they have taken your labor, which violates your determinism.
4. If someone takes your liberty, they have taken your self determinism.
5. If someone takes your life, then they have taken your self determinism in the future.
6. Since no one has the right to do those things, then they also do not have the right to delegate those activities to another, no matter how many of them there are.

But I'm not sure the first premise is reasonable or useful.

First of all, ownership is typically understood as a social construct. A person owns a particular thing just because that is the preponderance of opinion in a society (or would be the preponderant opinion if all individuals were to examine the social facts). People might or might not use some physical facts to come to that opinion, but it still remains: if most people in a society, and especially those with superior coercive power, such as the government, do not believe you own something, then you don't own it.

Thus, the sense of the premise "you own yourself" seems ambiguous. Does that mean a social construct does in fact presently exist? A social construct that should exist? An individual construct that individual Libertarians would like to exist? Or is it an objective fact: anyone who does not hold the idea of self-ownership is mistaken in the same sense they would be mistaken if they believed the Earth was flat?

Second, ownership is typically understood as a complex construct. It includes the components of positive and negative control, right to determine and derive benefit, right to destroy, and right to sell (alienability). Alienability is a legal principle that if I appear to give something to someone, but I don't give them the right to sell it, then I still own it. We do not, as typically understood, own something (at least not completely) if we do not have the right to sell it. Thus, if I really do own myself, then I ought to have the right to sell myself, which would seem to suborn slavery.

Third, it's just odd to use the concept of ownership to describe the self. Ownership is typically used to talk about the self's relationship to material objects; My self has a qualitatively, perhaps fundamentally, different relationship with my body and brain that it does with the material objects in my possession.

Fourth and finally, the premise seems either too restrictive or vacuous. Interpreted superficially, the statement, "You have sole ethical jurisdiction over your body, and self determinism," seems to preclude legitimatizing any coercion. If I really do have sole ethical jurisdiction over my body, than any coercion, even in self-defense or as punishment for infringing on others' ethical jurisdiction over their bodies, seems illegitimate. If someone want to kill someone else, it is illegitimate for me to interfere at all: I would be interfering with the would-be killer's sole ethical jurisdiction over his or her own body.

On the other hand, if we relax our conditions for legitimacy, then self-ownership becomes irrelevant. The real meat of the political philosophy would consist of the exceptions to self-ownership and sole ethical jurisdiction. The analysis, then, would ask why one exception would be legitimate but another illegitimate.

Even if the concept were coherent and internally consistent, I just don't see how one can derive anything but absolute law-of-the-jungle individualism from the premise of self-ownership. Self-ownership is a red herring; the premises from which anyone could derive a workable political/social system are all unstated.