Performance licenses aren't compulsory. No songwriter/publisher is compelled to join a performing rights organization, so not every copyright is available to be performed through a blanket license. Also, blanket performance licenses aren't "one size fits all," as the ISP tax seems to be in its current incarnation. They are tiered and variable, depending on the revenue of the licensee and the nature of their business. Also, one can contract around the PROs for performance licenses, through an organization such as Music Reports/Royalty Logic. The ISP tax proposal offers no such flexibility, as far as I can tell. I admire Professors Lessig and Felten very much, but, with all respect, I don't know if they've ever run businesses or done research in microeconomics. I think we need other voices in this debate.