Why do you say that Lessig's view of copyright law being a quid pro quo is mistaken? The Constitution itself says that the govt grants the rights in exchange for the authors promoting progress.
No the Constitution does not say that. It does not mention granting anyone any rights, nor does it require that anyone promote progress to get a copyright. It says:
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;
Most of the Founders had a view of natural rights in which rights are not granted by the govt. The govt only protects rights that people already have. It is Congress that promotes progress by protecting those natural rights (for a limited time, in the case of copyrights and patents). Note that the text says that Congress with secure the right, not grant it. Note also that it refers to their writings, as if the authors already owned them.
According to this, the UK has granted a perpetual copyright to Peter Pan. It should have been an example of why we should not harmonize with Europe.