I've been reading a number of different modern and classical thinkers on the Hobbsean/Lockean natural rights theory which undergirds the Declaration of Independence and our Founding. Many modern thinkers on both the left and the right simply don't take the theory seriously. They believe it to be just fictional rhetoric and itself riddled with internal contradictions. Even among those thinkers who do presently defend the theory, there is much disagreement on how the theory should be understood. And even during the founding era, there were variants on how to properly understand and apply the theory.
As the theory goes, men have certain "natural rights" in a state of nature (before civil government has been instituted). "Imperfections" in the state of nature (the fact that there is no police power with a monopoly on legal force to effectively enforce our natural rights) lead men to form civil society where they give up some of their natural rights -- that is trade their natural rights for civil rights -- to gain the security that only government can provide.
As John Jay put it in Federalist 2, "Nothing is more certain that the indispensable necessity of government; and it is equally undeniable that whenever and however it is instituted, the people must cede to it some of their natural rights, in order to vest it with requisite power."
The central question to be grappled with is: What is given up and what is retained? More socially conservative folks who defend liberal democracy (Walter Berns) tend to argue that we give up more to government and retain less. Indeed, it's only by virtue of trading our natural rights for civil rights, which can then be diminished by government, that makes liberal democracy defensible for someone like Berns, who writes in Making Patriots:
[T]he Founders generally knew, and...emphatically say in Federalist 2...when instituting a government, the people are expected to surrender "some of their natural rights, in order to vest [the government] with requisite powers." But [Justices] Holmes and Black are unmindful of this. Unlike Madison and the other authors of the First Amendment, they treat the constitutional right of freedom of speech as if it were a natural right, the right men possessed in the state of nature; there, as autonomous individuals, men might speak (and do) as they please without regard to political consequences because, there being no political community, nothing said (or done) could have political consequences. But, as the Founders made clear, that ceased to be the case when men entered civil society and formed a political community. pp. 136-7.
Moreover, in a letter to Commentary defending government censorship, he wrote, "One of the blessings of government is that it can, by due process of law, regulate what we say and print."
But even Berns recognizes that we don't surrender all of our natural rights to government, that we retain some.
It is, of course, true that he is required to surrender his natural rights when leaving the state of nature -- except of course, the few unalienable ones, the surrender of which would contradict the very purpose of the flight from nature -- but in exchange, as it were, he gains the security that only government can provide. For example, the Constitution makes it clear that he cannot be deprived of life, liberty, and property without "due process of law." Making Patriots, p. 19.
In reading Berns's writings, the only "right" which I've seen him identify as "unalienable" and hence one that government cannot regulate is that of conscience. Of course, in reading Madison's Memorial and Remonstrance, we see conscience clearly identified as an unalienable right.
But there is a problem, it seems to me, with Berns's analysis: "Liberty" (and "The Pursuit of Happiness" and "Life") itself, in its broad and general sense, is identified as an "unalienable right" in the Declaration of Independence. This, I think, is a reason why thinkers on the left and right don't take the Declaration seriously. For instance, as Robert Bork writes in Slouching Towards Gomorrah:
When they had won their independence and got down to the actual business of governing a nation, the Founders were not so lyrical [as they were in the Declaration]. The "unalienable Rights" of the Declaration turned out, of course, frequently to be alienable. The Fifth Amendment to the Constitution, for example, explicitly assumes that a criminal may be punished by depriving him of life or liberty, which certainly tends to interfere with his pursuit of happiness. p. 57.
It's not just right-wingers like Bork, however. Legal positivism is also deeply ingrained in leftist jurisprudence as well. For instance as Alan Dershowitz writes in America Declares Independence (his thoughtful book on the Declaration):
The rights stated in the Declaration, however, are so abstract as to be nearly meaningless. If Jefferson could indeed assert them as self-evident, it was only because they are stated in so broad a manner that their controversial application to any particular problem of policy is obscured by the fog of generality. Everyone can agree on the importance of rights to life, liberty, and the pursuit of happiness, but only because agreement about such sweeping terms amounts to almost no binding agreement at all.
For example, the abstract right to life is uncontroversial, but when reduced to its particulars, it provokes the most divisive disputes. This right has been cited by opponents of abortion, capital punishment, assisted suicide, war, deadly force, animal rights, and other hot-button issues. It also has been cited by proponents of abortion (the mother's right to life), capital punishment (the rights of future victims), gun control, just war, deadly force, and medical research on animals. The right to life has become an emotional cliche equally available to all sides on every life and death issue. p. 95.
Even back during the Founding there was disagreement on whether and how we bring our natural rights with us from the state of nature when forming civil society. For instance, as Philip Hamburger writes in Separation of Church and State:
Jefferson also changed the context of ideas in matters not involving religious liberty. For example, he asserted that individuals do not give up any natural right when entering into society. See Philip A. Hamburger, "Natural Rights, Natural Law, and American Constitutions," Yale Law Journal, 102: 907, 958 (1993). Although other writers adopted similar ideas, Jefferson's formulation was unusually dramatic. p. 146, footnote 5.
Let me wrap this up with an attempt at doctrinal coherence on natural rights. On the one hand we have Jefferson et al. (the more libertarian view) arguing that men retain their natural rights -- or at least, most of them -- even in civil society. And we also have Walter Berns's which is that we trade most of our natural rights for civil rights, save for the few "unalienable natural rights." Everyone I think agrees that we give up some natural rights and we retain some natural rights when entering into civil society. But if liberty itself is one of those "unalienable rights" which we retain when we enter civil society, then obviously we retain, contrary to Berns's assertion "very few" natural rights, many rights, indeed so many rights that they are unenumerable, hence the need to group them under the broad rubrics of "liberty" and "pursuit of happiness."
Another paradox: Liberty on the one hand is an unalienable right. But when entering civil society, we have to give up *some* liberty, don't we? Yes. Here is how I would resolve the paradox: Because men are by nature free and equal, and because men carry with them into civil society their unalienable natural rights, of which liberty itself, in its general and broad sense, is one, men only surrender to government that which is necessary to better protect their unalienable rights. Therefore, government by right generally has no legitimate power to involve itself in most concerns, certainly not ordinary "moral" concerns and certainly not to enforce a detailed, Thomistic understanding of the natural law.
The best scholarly work defending this theory of natural rights is of course Randy Barnett's Restoring the Lost Constitution. In it he argues, that when government acts, we must adopt a presumption of liberty, and the burden is on government itself to justify its actions and demonstrate that it is furthering the protection of our rights, which is why government exists in the first place.