A great Defence of Lessig by Ernie the Attorney leads me to Taking Copy out of Copyright which expresses clearly in legal terms what I have thought for some time - it is not copying that harms content owners, but re-distribution. The 'content' industry count each copy as a foregone full-price sale, which is odd economics.
The idea that they can prevent all copying by legally enforced technical means is wrong. What they should be doing is focusing on those who are making money from parallel distribution.
A thoughtful comment by 'pyramid termite' on the slashdot discussion thread:
The reason why organizations such as the mass media and the companies that distribute art were able to lock out live performers is that the "public" was reinvented -- instead of the "public" being anyone a performer could possibly meet, the public became anyone a mass media organization could reach by TV, movies, radio, print, etc.

Now the public is being reinvented again and is becoming anyone the artist or a fan of the art can communicate with. What we are seeing is not simply a war over copyright - it's a war over what the public will be and who will have the right to communicate with it. The mass media would prefer to have a public that remains large with easily controllable desires and means of distribution to it. The new public wants to control its own desires and means of distribution; it wants to be the artist, the publisher and the audience.

There can't be laws to enforce the old mass media copyrights without enforcing the old, outdated mass media model. This is not just a battle over who has the right to distribute a work but who has the right to distribute any work and who can create a public to communicate with. The performers would like to have their public to be anyone they communicate with - the mass media moguls are calling for laws against the technologies that would make this communication impossible.