Lessig's analysis ignores a key issue. Guns and copy machines can be used to break the law, but they are predominanly used for legitimate purposes. Software that breaks DRM encryption schemes is designed for one purpose only: to violate the contractual obligations of the purchaser. Similarly, Napster is only used to help people steal music without paying for it. Sure people COULD be using Napster to trade recordings of their own music, but they're not. So if you shut down Napster and outlaw DRM cracking, you are only eliminating illegal activity without eliminating any legal activity.
That being said, some of Lessig's lesser points appear strong to me. DRM software should not be allowed to take away the fair use rights of the copyright licensee. And I also find Sklyarov's arrest troubling, and am disturbed by Adobe's role in Sklyarov's arrest.