It is commonly asserted by the CopyLeft crowd that intellectual property protections have recently been expanded to such a degree that the public domain is under threat. In fact, it is asserted that the public domain is "shrinking."
Which is simply impossible.
Newly-protected works are not taken out of the public domain, and unprotected works are constantly being added to the public domain, to say nothing about all the works that have their protection expire every day.
There is no empirical evidence that the public domain is shrinking or in any danger. And there's no legal or even logical cause for concern about the public domain, either. Intellectual property does not keep creators from creating new works based on or inspired by protected works. IP didn't stop Fred Flintstone from being based on Ralph Kramden, and IP didn't stop Homer Simpson from being based on them both. It just stopped the new creator from stealing a character that someone else had created. The IP protection enjoyed by the creators of The Simpsons did not take Ralph Kramden out of the public domain.
All this concern about the public domain is nothing more than a bit of fear mongering rhetoric that is being used by the CopyLeft to undermine and attack intellectual property.
The real reason the CopyLeft has been making such a big deal out of protection the public domain lately is that they would like to do away with Technical Protection Measures (TPMs), such as digital rights management, etc.
The reason many people dislike TPMs is that it restricts their ability to make unlimited copies of digital content they have purchased. But there is no logical reason why consumers should assume that the purchase of a single copy of media gives them some sort of universal and perpetual right to the content for other applications.
If you own two houses and want hot water in both houses, you buy two hot water heaters. You don't buy one and then demand that because you bought one hot water heater for one house, the manufacturer ought to give you as many more as you want for free for as many other houses as you happen to own.
There is no reason why digital media should be any different.