Copyright terms have been extended over and over again. Corporations and sucessful (not to mention rich) artists claim that it is to protect their "right" to make money from something decades after it was produced. This is to the direct detriment of the public domain and our culture.
More than 95% of copyrighted material is out of print and thus largely unavailable, depriving us of knowledge and cultural heritage simply because the copyright holder is either not inclined to re-publish it or cannot be found. This material could be used by others to generate wealth for the economy, e.g. by re-issuing out of print books formatted for electronic readers or re-mixing music into something new.
The reality is that having a long copyright term harms artists and stifles creativity. There is less incentive for artists to produce new work when they can milk their old material for the rest of their lives (and probably their childrends.) Furthermore artists draw on popular culture for inspiration. They benefit from the public domain but expect not to have to contribute back to it for 70+ years. 15 years is more than enough time to exclusively exploit work.
Why is this idea important?
Shorter terms benefit everyone, except perhaps the executives of a few pubishing houses and record companies. The value to the public domain of currently unavailable work is immense, and the so-called "long tail" represents an immense opportunity to generare wealth for the economy.
It would also free artists from the constraints they find themselves in currently. In fact many circles already largely ignore copyright, much to their benefit. Examples include the fasion industry, the video games industry, the software industry and the music industry where similar works and obvious "influence" (or more simply copying) from other work is commonplace.
Furthermore the world is changing and the digital age has rapidly overtaken the law in this area. It would be far better to seek a healthy and workable balance than to try to turn back the tide.