Of all the creative work produced by humans anywhere, a tiny fraction has continuing commercial value. For that tiny fraction, the copyright is a crucially important legal device.
When government disappears, it's not as if paradise will take its place. When governments are gone, other interests will take their place.
A culture without property, or in which creators can't get paid, is anarchy, not freedom.
The real harm of term extension comes not from these famous works. The real harm is to the works that are not famous, not commercially exploited, and no longer available as a result.