For many years, I held a strong position against the copyright based on the effects of enforcing copyright on freedom of speach in the internet.
However, recently I read Rothbard's Man, Economy, State, where he makes following point: when you purchase a work with a statement saying "copyright", you agree not to copy the work without the prior authorization by the copyright owner, and on free market copyright violations would be prosecuted as contract violations.
This strikes me as a really strong point for the protection of the copyright.
Now I'm looking to hear some really strong arguments against copyright, preferably based on principles of free market and Austrian economics