In the modern theory of growth, monopoly plays a crucial role both as a cause and an effect of innovation. Innovative firms, it is argued, would have insufficient incentive to innovate should the prospect of monopoly power not be present. This theme of monopoly runs throughout the theory of growth, international trade, and industrial organization. We argue that monopoly is neither needed for, nor a necessary consequence of innovation. In particular, intellectual property is not necessary for, and may hurt more than help, innovation and growth. We argue that, as a practical matter, it is more likely to hurt.
He also has chapters from a future (and much less technical) book on his page, do have a look if you are interested in the issue.
It's quite hard to find evidence that the current system is doing any good (except to lawyers bank account), but there's a lot of inertia since the damage to the general public is not perceived as big enough yet (because only poor people die because of high drug prices, or because everyone now thinks that software and operating systems can only be full of bugs and programs not working together). Fighting inertia requires lots of work especially since the benefiting crooks very close to power (lawyers).
