Why stop online piracy?

Matthew Yglesias argues that a little copyright infringement is actually good for our economy, and makes the connection between libraries and secondhand bookstores. Money quote:

After all, things like public libraries, used bookstores, and the widespread practice of lending books to friends all cost publishers money. But nobody (I hope) is going to introduce the Stop Used Bookstores Now Act purely on these grounds. The public policy question is not whether the libraries are bad for publishers, but whether libraries are beneficial on balance.

Additionally, Hollywood is deluded if it truly believes that the reason for its financial woes is the rise of online piracy. The critic Roger Ebert passionately makes the case in his recent piece on the subject: ticket prices are too high, the moviegoing experience is poor, and they're not actually making very good films.