The copyright term is automatically too long if my anyone who would benefit from it entering the public domain is dead.
We have at least one corner of the universe where we've defeated scarcity. We can't run out of music. Hell, we can't even run out of a specific recorded performance, if even the most trivial efforts of due-diligence backups are performed. We should be proud-- we're at least one step on the way towards Star Trek replicators and universal abundance.
But the current system is so tied to the idea of "markets" and "ownership" that only really make sense for scarce physical goods, that we ended up having to force everyone, under threat of law, to treat a limitless resource that's part of our shared cultural experience, like a rare physical widget that must be owned, sliced up, and sold under restrictive covenant.
We should be taking all the money going into the content business-- all the funds being spent on the production of movies, music, novels, art, potentially even software-- and use it to bankroll an enormous centralized endowment for the creative community.
This immediately silences all "but how will artists eat?" strawmen. Even if you're not a live-show performer or merchandising expert, you get paid by the endowment on a predictable stipend basis, rather than having to hope you can effectively monetize a package of "rights" while dealing with an industry full of middlemen out to rip you off.
This would ensure that many, many more artists can live their passion-- how many great but unknown bands could spend their lives touring, if we took the money that bankrolled Taylor Swift's tour and sliced it up into 50k-per-person-per-year grants? How many sculptors could we keep on the books for the price of one Anish Kapoor? It would also be interesting to compare efficiency of funds delivery-- replacing a bunch of for-profit publishers with a single cooperative or state-run entity probably results in more dollars actually reaching artists overall.
It also avoids the perverse incentives on the other side-- if you make one world-breaking hit, you can't ride it forever. Just because you sung White Christmas once doesn't mean you get out of ever having to work again. If we eliminate the opportunity to slice and subdivide "rights" to a work, then there's no incentive to hold back maximum utilization of it. Imagine the improved utility of modern content services if they can get legal access to all the things-- Netflix and Hulu would have to compete on the best infrastructure, UI and tooling, rather than "only we have Futurama".
Don't get me wrong, I like the idea of abolishing copyright and funding art more directly but I also don't see the point in the goverment deciding what is and isn't art. At that point perhaps its better to ensure that everyone was a livable universal basic income and let people create art if they want to use their time to create art. And on top of that you can still have patronage / grants if you want specific types of art created more than they would otherwise be.
If your band tours to public parks or empty bars, you still get a living wage. If you crank out six paintings a month but they just line the halls of public libraries because nobody really wants to buy them, you can still live on the stipend.
More importantly, it eliminates the need to create that ownership right, and impede any "descarcification" tactics. Yes, those tangible things might be somewhat scarce, but if someone starts making posters of your paintings, or a recording of your concert goes viral, you both have no reason and no legal method to stop that from happening.
These don't rely on copyright so wouldn't need any special consideration when abolishing it.
As far as society is concerned, society’s resources (police, courts, etc) should only be given up to the point that the incentive to create works of art exists.
At zero copyright length, we can say artists (and media creating/owning businesses) have less than a desirable amount of incentive to create (from society’s perspective).
At 100 years, we can easily say there is too much incentive to seek rent and rest on one’s laurels.
The most expensive works of art covered by copyright right now are big budget Hollywood movies and tv shows. If these businesses would continue to make them with a 20 year copyright term, then 20 years should be the max. And I might even say they would continue to make them with a 10 year term.
Can we? What is the amount of art that we want to be created? How much more art do we really need every year considering that old art can be infinitely reproduced in the digital age? Remember that the art output without copyright is well above zero since we had art before copyright.