A common view among anarcho-libertarians is that the Constitution of the United States is not a binding "social contract" -- and never has been -- because
- the Constitution was imposed on many Americans who were not parties to its ratification or who opposed its ratification, and
- regardless of the circumstances of the adoption of the Constitution, one generation cannot impose a contractual obligation on later generations.
I have addressed those objections before, but I have further thoughts.
As to the first objection: Consensus on any set of complex issues is impossible. But why should that prevent a majority from imposing its rules on a commingled minority whose adherence to the rules is necessary to the attainment of their purpose? If that purpose is to establish a regime which fosters liberty -- requiring, among other things, a commitment to mutual defense -- it would be foolish for the majority to lessen its commitment to liberty for the sake of assuaging the minority. Opponents of the regime cannot claim to be oppressed if the regime allows them to express their opposition peacefully, which the Constitution does.
Moreover, the original Constitution became effective only when ratified by three-fourths of the signatory States (nine of the twelve States that sent delegates to the Constitutional Convention). And it bound only the ratifying States. The other three States (plus Rhode Island, which did not send delegates to the Constitutional Convention) could have refused to ratify it -- as New Hampshire, Virginia, New York, and Rhode Island nearly did -- and could therefore have remained outside the Union. (Click here for a chronology of the States' ratifications.)
As to the second objection: The Constitution allows for amendments. (Click here and scroll down to Article V.) An amendment may be proposed by two-thirds of both houses of Congress or a two-thirds of the delegations of the States meeting in convention. An amendment must be approved by three-fourths of the States. The only matter now beyond amendment is "that no State, without its Consent, shall be deprived of its equal Suffrage in the Senate." In other words, the Constitution can be changed by essentially the same process by which it was adopted: three-fourths of the States must agree to an amendment. But, thankfully, the Constitutions cannot be changed easily, in response to whims and passions that might diminish the Constitution's guarantees of liberty.
So, yes, one may object to the Constitution, one may refuse to concede its legitimacy, and one may object to being forced by the state to abide by it. But here's the catch: Such objections and reservations are valid only to the extent that the Constitution actually deprives one of liberty. Inasmuch as it does not do that (except in the fevered minds of anarcho-libertarians), and inasmuch as it fosters liberty, such objections are nothing more than irresponsible tantrums masquerading as a political philosophy.
Most of us are glad of the Constitution and accept it as a bulwark of liberty. The anarcho-libertarian alternative is anarchy, which is a way-station to warlordism and dictatorship. I fail to understand why a small (crackpot) minority should be relieved of its false sense of oppression so that all of us might "enjoy" the "benefits" of anarchy.
For more about the impossibility of peaceful, libertarian anarchy, read these posts:
Defense, Anarcho-Capitalist Style
But Wouldn't Warlords Take Over?
My View of Warlordism, Seconded
The Fatal Naïveté of Anarcho-Libertarianism
QandO Saved Me the Trouble
An essential ingredient of anarcho-libertarianism is the non-aggression principle, which I address here:
Libertarian Nay-Saying on Foreign and Defense Policy
Libertarianism and Preemptive War: Part I
Right On! For Libertarian Hawks Only
Understanding Libertarian Hawks
More about Libertarian Hawks and Doves
Sorting Out the Libertarian Hawks and Doves
Libertarianism and Preemptive War: Part II
Give Me Liberty or Give Me Non-Aggression?
More Final(?) Words about Preemption and the Constitution
"Peace for Our Time"
Idiotarian Libertarians and the Non-Aggression Principle
Contrary to anarcho-libertarians, liberty is not an essence that wafts from heaven to imbue our souls. It is a set of compromises about how we live with each other. To more deeply explore the meaning of liberty and the proper role of the state in assuring it, read these posts:
Practical Libertarianism for Americans (links to a series)
The Meaning of Liberty (a series gathered in a single post)
Actionable Harm and the Role of the State
Finally, there is Varieties of Libertarianism, which summarizes and compares the tenets of anarcho-libertariansim (or anarcho-capitalism as it is usually called) and the other main branches of libertarianism.