The Congress shall have Power ... To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries.
This clause clearly establishes intellectual property as a granted right, not a recognized or fundamental right, that is, the "right" to "intellectual property" does not exist unless explicitly granted by Congress at its discretion. Furthermore, Congress is constrained to grant this right only in service of a specific purpose. namely, to promote the Progress of Science and useful Arts, and only "for limited times".
Notwithstanding that the Supreme Court has effectively eviscerated the "limited time" constraint in the case of copyright, "intellectual property" is clearly on a different legal footing from the "inalienable rights" to "life, liberty and the pursuit of happiness" to which people are endowed by their Creator, as recognized in the declaration of Independence. Neither the Declaration nor the Constitution mentions "property" by name [correction: the 5th amendment does mention it. See the comments.], but it is quite clear that the right to physical property was universally considered an inalienable fundamental right by the Founders. To cite but one of many examples, the state of Rhode Island attached a signing statement to its ratification of the Constitution that reads in part:
We, the delegates of the people of the state of Rhode Island and Providence Plantations... do declare and make known,—
I. That there are certain natural rights of which men, when they form a social compact, cannot deprive or divest their posterity,—among which are the enjoyment of life and liberty, with the means of acquiring, possessing, and protecting property...
Rhode Island's signing statement is significant because it is quite lengthy. It contains 18 separate clauses explicitly recognizing a long list of fundamental rights. (It's actually worth reading in its entirety). It is reasonable to suppose that if Rhode Island took issue with the clear implication of the Constitution that "intellectual property" is not a fundamental right, they would have said so.
The arguments against SOPA are mainly based on the collateral damage that would accrue by giving content "owners" the power to indiscriminately shut down web sites without due process. But this argument tacitly concedes a much more fundamental point, which is that a grant of copyright is not a right but a privilege granted at the discretion of the People for a particular purpose. It is far from clear that the Constitutional requirement that exclusivity be granted "To promote the Progress of Science and useful Arts" is being met.
Political arguments are often lost before they even start because one side allows the other to frame the debate. The clearest example of this is the tacit acceptance of the terms "pro abortion" and "anti abortion" in the debate on reproductive rights. In this case, the tacit acceptance of the term "intellectual property rights" concedes the fight before it starts. If there are intellectual property rights, then the debate can only be about the extent to which the state should go in order to defend those rights. But, as I have shown above, there is no legal basis for intellectual property "rights", only intellectual property "grants" (for limited times and for a specific purpose). I hope it's clear how this reframing would change the tenor of the debate.
[UPDATE:] OK, so not everyone has missed this :-)
[UPDATE2]: Wow, things are changing fast: "In an incredible turn of events, six Republican Senators have asked Majority Leader Harry Reid not to hold a vote on PIPA, the Senate version of SOPA...."
[UPDATE3]: Someone who goes by the handle Nirvana over on Hacker News makes a really excellent point in the context of conceding too much by adopting the wrong terminology:
...the Bill of Rights was enacted "in order to prevent misconstruction or abuse of its powers". This is referring to the limited powers granted to the government in the constitution. Notice, the preamble doesn't say "in order to grant rights...". The bill of rights contains "further declaratory and restrictive clauses".
Thus, these clauses are not designed to create or grant rights, but are of a "declaratory and restrictive" nature.
The constitution does not create any rights. There is no such thing, in the american form of government, as "constitutional rights". [Emphasis added.] People often use this phrase when referring to the Bill of Rights, but it is imprecise, because the Bill of Rights doesn't grant rights. IT doesn't say "the people shall have the right of free speech", instead it says "Congress shall make no law ... abridging the freedom of speech, or of the press;"
The right of free speech, as recognized by the First Amendment, precedes and predates the constitution.