The state of YouTube proves that the copyright industry will not accept such a world. They want the technology industry to prevent copyright infringement from happening. They don't want to have to sue anyone after it has happened. Copyright infringement is widespread, decentralized and international so legal threats simply don't work. Prevention is the only option.
Copyright infringement prevention is only possible if they seize control of our computers. That is morally objectionable and cannot be allowed to happen even if it destroys the copyright industry.
> how do we get the benefits of the GPL - especially receiving things like source code - if we no longer have copyright?
We don't. The GPL was created by Stallman in reaction to copyright protection being extended towards source code. Without copyright, the software development world might revert to what it was like before that event. I don't fully understand what it was like in those days but there are descriptions in his books.
It’s not obvious to me that enforceable copyleft licences have increased the availability of free software to such an extent as to outweigh the loss of freedom effected by normal copyrights. Abolishing copyright (or less radically, rejecting the prevailing interpretation of copyright law which says that software is a “literary work”) would do more to advance the four essential software freedoms than any copyleft licence. Notably, copyright is the only thing standing in the way of freedoms 2 and 3. As for freedom 1, companies would still treat their source code as a trade secret, but without copyright they’d have no recourse against people republishing leaked source code, which could then be incorporated into free software projects.
I think this was probably more of a critical mass sort of thing. Historically, it seems like copyleft licenses (and perhaps even GCC's horribly byzantine internal architecture) probably played a key role in getting free software off the ground. Once you have sufficient mind share though it no longer seems to be as necessary.
I'm not sure this is true. The publishers aren't demanding that Internet Archive add DRM to their e-books - they're demanding that Internet Archive stop distributing them entirely. I can certainly imagine a world where DRM-free e-books are the norm and unlicensed distribution is limited only by legal threat and not by technical means. Yes, the fact that information can now be copied instantly for free (it could previously be copied with some time and effort with a photocopier, or with typewriters samizdat-style, or with pen and paper monk-style) means the publishers are less confident that legal threat will be enough... but we did mostly end up in a world where DRM-free music is easily available.
But also, physical books aren't going away. As long as you can buy physical books, you can participate in a world of copyrighted books without running DRM agents on your computer. You miss out on some potential 21st-century gains like having the text of the book in electronic format and being able to share it without spending some time at a scanner, but you haven't lost anything you had in the 20th century.
(Also on the topic of computing freedom, how do we get the benefits of the GPL - especially receiving things like source code - if we no longer have copyright?)