It is not true of all laws. Some legal concepts and rights transcend the existence of government and the threatened use of force on its behalf. For instance, the rights enumerated in the 1st and 2nd Amendments to the U.S. Constitution exist regardless of their presence in the document itself. You have the right to speak and defend yourself by virtue of your being a human being. It's not a right granted you by the Constitution or any other legal document.
On the other hand, Patents, Copyrights, and Letters of Marque exist wholly as creations of law and other legislated instruments. All three of these concepts entirely consistent with the Constitution, and in fact are listed specifically as such in the document, but none of them are actual rights. They are legal fictions created because we, as a society deem there to be societal benefit of their existence. If we, through our legislatures decide to alter or abolish those concepts, it is perfectly legal for us to do so.