Earlier quoted context omitted.
Author’s life is too long. Surely, 20 years is far sufficient to incentivize creating media, although I would err on the side of 10 years. The copyright term is automatically too long if my anyone who would benefit from it entering the public domain is dead.
I think (but could be convinced otherwise) that the term is less important than the restrictions. More liberal definitions of fair use, for example, or clarity on when something is a copy or a derivative (like with people getting sued for vaguely similar songs) would be better. The work is always the authors, I'm less concerned about them retaining some kind of claim on it, especially if they're still actively using…
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.