See this post from Right Reason, where Ed Feser criticizes the concept of "self-ownership" as a libertarian underpinning.
In any event, my current views by no means rest entirely on the SOP. I would also now argue that, whatever one thinks of the SOP, the thesis of self-ownership itself is inherently indeterminate. Its history alone indicates as much. Most contemporary libertarians take the principle to imply that each man has absolute sovereignty over himself, and has a right to engage even in immoral actions -- suicide, drug use, etc. -- as long as these do not harm anyone else. But John Locke, whose advocacy of the principle has influenced so many libertarians, would have utterly rejected such a notion. For Locke, talk about "self-ownership" is really just a kind of shorthand for the leasehold rights God has granted us over ourselves as stewards of His property, and we have no right to do anything to ourselves which might damage that property. Hence Locke's famous claim that no one has a right to commit suicide or to sell himself into slavery (a claim that is crucial to his case for limited government, since if we have no such rights over ourselves, we cannot transfer them to government).
The key point is that to own something is just to have a bundle of rights over it, so that any theory of ownership (whether of ourselves or of anything else) presupposes a theory of rights. Moreover, people can own something without having an absolute right to it: hence someone who has paid off his mortgage really does own his home -- no one can take it from him or enter the premises without his permission, etc. -- even if there are easements on his property that put certain limits on what he can do with it. So any theory of self-ownership must begin by specifying exactly which rights we have over ourselves, and why; and only if it can show that we have over ourselves every possible right that could enter into ownership of a thing will it thereby show that our ownership over ourselves is full and absolute. If it shows instead that we have many or even most of these rights but not every single one of them, it may entail that we have a kind of ownership of ourselves, but not full and absolute ownership. In short, no appeal to self-ownership can suffice, all by itself, as an argument for libertarianism, or even as a way of giving determinate content to libertarianism, since the content of self-ownership can only be determined by a prior theory of rights.
Locke's theory of rights, given its foundation in our obligation to preserve God's property, yields an account of self-ownership that is clearly less than absolute. Alternative theories of rights might also yield less-than-absolute views of self-ownership. In particular, I have suggested that if rights are grounded in classical Thomistic (as opposed to Lockean) natural law theory, then this is bound to put even greater limits on self-ownership. For if, as some classical natural law theorists would argue, the function of rights is to safeguard our ability to realize our moral obligations and natural ends, then there cannot be such a thing as a right to do what is of its nature contrary to our natural ends and moral obligations. That doesn't mean there might not be reasons (even moral ones) for not interfering with the use a person makes of himself and his body, talents, and abilities. But it does entail that no one can have a natural right to do what is inherently immoral or contrary to one's natural ends, so that no one's self-ownership can be absolute, if that is meant to imply that one has a natural right to do whatever he wants to with himself as long as it hurts no one else. Whether this yields a version of self-ownership that can still be called "libertarian" (as I thought it did in my JLS article, though I no longer think this), it indicates that if, as many libertarians think, self-ownership is the central premise of libertarianism, then "libertarianism" is a very fluid concept indeed.
Contrast Feser's theory with Harvey Mansfield's argument about Locke and self-ownership:
Locke gives two descriptions of the character of men in their fundamental relation to liberty. He says that they are the "workmanship" of God, that men are "his [God's] property" and so belong to God; but he also says that "every man has a property in his own person."1 These appear to be directly contrary because the "workmanship argument" (as it is called by Locke's interpreters) would make man a slave of God2 whereas the idea of property in one's own person sets him free to do with himself what he wishes. Thus Locke says, in accordance with the former, that men have no right to commit suicide ("everyone is bound . . . not to quit his Station wilfully"3). But in accordance with the latter, though saying nothing directly about a right of suicide, he pronounces that in the state of nature, man is "absolute lord of his own person and possessions."4 Yet Locke does not make a point of the contradiction between these two descriptions. It is rather as if he had forgotten what he said earlier or perhaps lost his train of thought. Yet Locke does not seem to be a woolly-minded fellow, and his reputation shows that both his friends and his enemies take him seriously. His political thought typically contains contradictions, of which this one is perhaps the most important, but he leaves the reader to do the work of establishing the contradictions and working out their implications. In this case and in other cases, Locke does not leave the contradiction as flat as I have reported it; he teases readers with possible routes by which it might be harmonized.5 But most of all, Locke lets readers do their own harmonizing by allowing them to combine two things they want to believe. Almost all of Locke's readers would want to believe in the truth of Scripture, and many of them would like to think, or might be persuaded to think, that their belief is compatible with, or even entails, the notion of liberty that Locke sets forth.
The difference between belonging to God and belonging to yourself is not a small one....
Whether Locke was deliberately playing games with language, the kernel of Truth in Mansfield's theory is as follows: Some thinker comes forth with a revolutionary idea -- like Locke and self-ownership -- and explicates the idea in a particular way; but the idea then evolves beyond the original explication (or original expectation). The idea won't evolve randomly; often the idea unfolds in ways consistent with its original premises. One could easily see, for instance, if an individual owns himself, as Locke argues, that one does indeed have the moral and natural right to commit suicide or take drugs or do whatever he wants with himself-- his property -- so long as in doing so he harms no one else.
Indeed, in Bowers v. Hardwick, Justice Blackmun's dissent uses the self-ownership premise to argue for a "right" to commit sodomy because he believed, as did Locke, "that a person belongs to himself and not others nor to society as a whole."
Or take Locke and religious liberty. As I wrote in this post:
Locke, although not the first to argue for religious toleration, is without question the most important philosopher to America's notion of religious liberty: Locke formulated the notion that men have unalienable free and equal rights of conscience. Madison and Jefferson could not have argued for religious liberty as they did had there been no John Locke. But Locke, in his personal position, didn't believe in extending tolerance to, among others, atheists or Catholics! However, when Jefferson and Madison took Locke's ideas, they expanded them in the spirit of Locke, to apply universally. After all if "all men" have unalienable rights of conscience, why shouldn't Catholics or atheists possess such rights equally? Are they not human? As such, "Lockeans" Jefferson and Madison asserted that religious rights extended to "the Jew and the Gentile, the Christian and Mahometan, the Hindoo, and Infidel of every denomination."
Indeed, Locke gave what he thought were good reasons for not extending rights to Catholics and atheists; but as soon as his idea began to evolve in the minds of our Founders -- Jefferson and Madison -- they just didn't hold up. Similarly, there is no good reason to believe (or Feser gives us no good reason) that we must view the concept of self-ownership exactly as Locke argued in the 17th Century -- "that 'self-ownership' is really just a kind of shorthand for the leasehold rights God has granted us over ourselves as stewards of His property, and we have no right to do anything to ourselves which might damage that property." For one, Locke was, as Alan Kors once put it, an "archetypical empiricist," and proving that God exists (whether Locke's conception of God or Feser's) is no easy task.
Whatever theory for which we advocate ultimately will rest on a moral premise that is unproven and unprovable in an empirical sense. So it wouldn't therefore be unreasonable to "scrap" the God part of the self-ownership principle and simply assert that an individual belongs to himself simpliciter (and if it's because God says so, then it's because God says so). "[A]nd then draw logical and necessary conclusions from those principles." But when we do this, we might "discover" that, gasp!, an individual really does have "a right to engage even in immoral actions -- suicide, drug use, etc. -- as long as these do not harm anyone else."