The problem with eternal copyrights is that big corporations wind up owning the shared culture, and you are not allowed to build on what went before and make it your own.
I say copyright should end with the death of the original author, or seventy years, whichever comes first.
People get sued for singing "Happy Birthday," for God's sake. That song should be in the public domain.
Walt Disney has been dead for fifty years. He got his fair share from his copyrights.
I would see no argument with this as well, with the exception that 70 years is a recent extension, and is far longer than it should be.
Importantly, there are such vast quantities of library copyrights and patents, there would be a gigantic amount of content released all at once. So the value of entire genres of material would be tiny, unless they were value-added with superior editing, for example. Like Criterion Collection movies today.