Surely you end up with one abstraction (of ownership) each. If you teach me some idea, I still know it even if we've agreed that I won't teach it to others for profit.
> If we exchange ownership of ideas, we end up with one idea each
How would that work? Given that one exposed to an idea, a person cannot exactly erase it from their mind...
I mean if I have an idea and I give it to you the idea itself is still in my mind. And in order to give it to you I have to communicate it to you, so now it is in your mind too. So innately, while physical objects are physically moved, ideas are only ever copied; the former creates a sense of ownership because when a brick is in your hand it is not in mine, whereas the latter makes this notion of ownership impossible.
Let's try anyway. If I write the idea on a piece of paper, zip it into an envelope, and give the envelope to you, not only do I still have the idea in my head but can you really claim to somehow "have" the idea too? Unless you open the envelope and you don't get to actually "have" it, you have an envelope which contains a copy of the idea that's still in my mind and not in yours. You don't even know what I've given you unless I shared the idea with you beforehand, at which point we're back to square one and the piece of paper is moot (it may carry more detail but that's immaterial to the concept of ideas fundamentally being only copied).
A person has an idea and writes it on a piece of paper, puts it in an envelope, gives it to me, the person dies, I don't ever open the envelope and then I give it to you. Did I ever "own" the idea? I don't even know what it is? A copy of the idea has disappeared when the person died, the piece of paper has a copy on it, and once you read it that idea will be in both in your mind and the paper until you burn the latter.
So maybe you're thinking, but the person of origin of the idea matters. Okay, let's go along with it. Say you and I never even remotely interacted, and I come up with a "foobarbaz" idea and you come up with a "foobarbaz" idea, and we happen to meet. We exchange ideas and realise "oh we had the same idea!"; how can the idea be "the same" if it has been independently conceived and the person of origin matters? To double down on that, after the transactional exchange, we both have one "foobarbaz" idea , not two identical ones each: the operation was a complete noop.
We could drill down further about whether any idea can ever be truly original or if it's about standing in the shoulders of giants, so a huge proportion of any idea or the process having led to is is actually not original at all but instead remixes.
All this to essentially say that "ownership of ideas" and "usage rights" are really a completely artificial construct, one that aims to replicate ownership as it is born out of physical reality.
Which brings me to TFA's situation, in which half a million books are essentially disappeared purely for the sake of pretending ideas are like bricks, as in they should be "owned" because someone could make money off of it, which is not even true because even if I wanted to throw a truckload of money at these folks they would still not allow the ideas to be accessed because they can't be bothered to republish - even though they can be bothered to sue - so the paper/bits might just as well be set on fire, which is most certainly not what the authors would have desired.
PS: Obviously authors deserve tools that help them make a living and combat plagiarism, but this situation is way beyond that and highlights how these artificial constructs are completely upended to the detriment of all.
If I sell you copyright of my code, I might still have it on my computer but I lost any rights to use it. This is a standard business arrangement that anyone on this site knows and uses. I don't think it's as complicated as you make it sound.
I think the opposite is more irrational. I want to be able to sell my work, and I want to own my work for myself too, otherwise I have no chance of competing against the big corporates. GPL licenses don't make any sense if the authors don't control the copyright, so open source would die.
Yes, it's arbitrary - just like practically everything else. Having to drive my car on a road and not kill anyone is arbitrary, but leads to good outcomes.