The United States Constitution is often lauded as the epitome of freedom. And indeed, the U.S. has for most of its history sat far towards the "more free" end of the spectrum of actual governments. The original Colonies, Articles of Confederation, and the first hundred years of the United States Constitution were, with some glaring exceptions, among the most libertarian of governments in human history, and far more libertarian than the modern United States. The actual text of our Constitution, read straightfowardly under standard English definitions, or read as most lawyers read it when enacted, is (with the exception of the Sixteenth Amendment, the income tax) a fringe libertarian document. Of all the 2008 Presidential primary candidates only the libertarian Ron Paul could credibly base his platform on the actual text and original meaning of the Constitution. The positions of all the other major candidates, as well as the interpretations of most of our Supreme Court justices, depart very far from the actual text in its original meaning.
But our Constitution is nevertheless deeply flawed. In a number of ways it facilitates our slow slide into socialism and tyranny. It is rather easy for Congressmen, Presidents, and federal justices who wish to interpret it as granting broad powers and narrow rights to do so, and they have been doing so ever since the Constitution was enacted. A wide variety of other constitutional mechanisms and institutions would do a far better job at slowing and reversing the death of liberty in the modern world.
Much of the early liberty of the American Colonies and the early United States was, as Adam Smith observed, due to low exit costs. Farming was the dominant economic activity, and the availability of free land out West made it relatively easy for a farmer to move if the local conditions got too oppressive. Officials had to preserve liberty to keep their populations. Nevertheless, our Constitution among other factors kept the U.S. more libertarian than Russia, which also had a large frontier. Our Constitution slowed, but did not stop, the aggrandizement of power into effectively unaccountable and increasingly oppresive forms. While there are many more ways to make it worse than to make it better, and this author does not recommend constitutional convention or military coup, those trying to set up new constitutions, or amend their old ones, should observe that there are a number of crucially important ways in which the U.S. Constitution can be improved upon.
Speaking very broadly, the general problem with our Constitution is that it allows the rise of a fully sovereign and monolithic federal power. Such an entity inevitably aggrandizes its power and ultimately cannot make credible commitments to protect property or any other rights or powers that it covets for itself. This is a common flaw of modern constitutions, but there are a number of protective mechanisms which these constitutions do not employ, or employ incorrectly, that could be brought to bear to correct this general problem.
A bit more specifically, here are most of the major flaws in the U.S. Constitution:
(1) The legislative branch is too powerful: several of the grants of power in Article I are too broadly worded and the rules for interpreting them are insufficiently strict. Once legislatures have achieved broad powers, they can hardly be expected to vote to give those powers up. It's a one-way ratchet towards socialism and tyranny.
(2) The executive branch is too powerful: executive duties are not well defined and the non-delegation doctrine is not enforced, allowing the rise of permanent unelected lawmaking bureaucracies. (In many practical ways the real constitution the post-New Deal U.S. operates under is the Administrative Procedures Act, augmented by things like Chevron deference).
(3) There is far too much use of elections and far too little use of lotteries. A number of officials should be chosen by lottery (as in ancient Athens) or by a sequential election/lottery cycle (as in the Venetian Republic). Lotteries can be very good at solving public choice problems, such as the problem of concentrated lobbying during elections which trump widely distributed preference.
(4) One of the two gravest defects lies in how courts are structured with respect to the constitutions they interpret. A basic design pattern for good government is that officials should not be interpreters of their own power. Allowing federal courts to interpret federal powers and state courts to interpret state powers has led to inevitable aggrandizement of the powers of both: to broad interpretations of power-granting clauses. Vague constitutional language, which is practically inevitable, would not lead to tyranny if the judiciaries who have final say interpreting these clauses did not have incentives to expand these powers. This effect is exacerbated by allowing the legislature and executive to choose the judges. I am afraid that, for example, Professor Barnett's proposal for convincing federal courts to (in many ways return to) libertarian interpretations of our Constitution, desirable as such interpretions are, is nevertheless futile. Incentives operate to select judges who profess broad interpretations of power, and while sitting on the court for judges to further aggrandize governmental power. Our judicial structure is another one-way ratchet towards tyranny.
A much better (but hardly the only better) proposal for selecting judges: select judges for lower courts by lottery from among lawyers who have scored in the upper percentile on the state bar exam and have been practicing for at least 5 years. Select judges for higher courts by a lottery over the judges of lower courts who have at least five years experience on the bench. Judges can still be impeached and removed for by legislatures or independent tribunals for egregious illegal behavior, but the executive and legislature play no role in selecting judges in the first place. This makes the judiciary far more independent of the executive and legislative branches.
The basic structure of courts in the American colonies was far better than our structure under the Constitution. There, the Privy Council, not colonial courts, had the final say in interpreting colonial charters. Being more dependent on Parliament and the Crown than on the colonial legislature, it had no incentive to aggrandize the power of the colonial legislatures. There were also a number of flaws in colonial government, including deep flaws in the British constitution that allowed the rise of Parliamentary sovereignty, which both compromised the independence of the Privy Council and trespassed on colonial legislative powers. There was also the practical problem of distance that made appeals to the Privy Council in London far too infrequent. But the basic appeals structure was far superior to that of our current Constitution. The colonial court structure will work far better now without the delay problem and if the highest court is not itself tied to a legislature.
(5) The other of the two gravest defects is the lack of unbundled political property rights. Federalism and separation of functions are two very good, indeed crucial, features of the Constitution, but they are insufficient for protecting liberty. Unbundled rights to engage in narrow forms of coercive legal procedure are often a far better way to distribute power than hierarchical federalism and separation of powers in an entity that is supposed to be in totality sovereign. The gothi of medieval Iceland, often cited by anarcho-capitalists, were an example of a political property right. Medieval and Renaissance England was a world full of polycentric, or highly distributed, political property rights, but these were swallowed up by legislative powers in colonial America. We must revive this very important and legally mature method of distributing political powers. Many legislative, executive, and judicial functions should be granted to private entities as political property rights, with the jurisdictional boundaries and procedural standards defined in those rights to be enforced by an extraordinary court independent of all other governmental entities.
(6) Insufficient protection is given to, and scope allowed for, choice-of-forum and choice-of-law clauses. Much, though by no means all, law could be entered into by contractual agreement, allowing for healthy forms of legal competition in certain areas, such as contract and family law.