It is in the interest of culture to have a large and dynamic public domain. The greatest classics of Disney were all based on stories in the public domain, and Walt Disney showed how public domain ideas and characters could be leveraged by others to bring enjoyment and money. But ironically, after Walt died, the Disney corporation became the major backer of the extended copyright laws, in order to keep the very few original ideas they had — like Mickey Mouse — from going into the public domain. Also ironically, just as Disney was smothering the public domain, their own great fortunes waned because they were strangling the main source of their own creativity, which was public domain material. They were unable to generate their own new material, so they had to buy Pixar.
[You reap what you sow.]
Source: The Technium