That specific argument has been made a lot of times and overruled as many times. Don't be so naive, a world without copyright could perfectly work. It would just be very, very different. It's not like anyone wants just the complete abolition of copyright law to happen, and nothing else, obviously that wouldn't be very fair. You're misrepresenting the situation by depicting a world just like ours, with the single difference that you'd be free to steal the work of an author.
Think about an analogous situation. If you would have told people 40 years ago that a variant of Unix would be made, completely open-source and free, and with large companies working on it too, not just some hobbyists, would they have believed something like that is possible. And yet, Linux still exists. I know copyright is very relevant for Linux (GPL etc...) but I want to show that it is possible for completely other systems to develop than the traditional, where you pay for an (unexpirable) license on the copyrighted work which is kept completely proprietary with some fair use additions.
In any case, fixing copyright doesn't seem that hard. In a world with copyright, which is perfectly fine by the way, the term could be much much shorter. >70 years is a disaster. 7 years seems fair and I think it would vastly enrich our culture, for a very small price to the creators of original work. Obviously it's more complicated than that, but that seems like a good start.