> Author's life + 20 years would be acceptable in my opinion. That would ensure that the author's offspring are adults and can take care of themselves.

But that's not the purpose of copyrights.

The purpose is to encourage the creation of creative works for society.

You cannot encourage new creative works from a corpse.

You have to think "At what point does the lack of a copyright future, prevent this person from creating it in the first place?"

And the answer is probably 5-10 years. You've milked it all but dry after 5-10 years.

How much money does a movie make 5-10 years after it's published? A trickle. Not enough for a studio to say "Well if it's only 5 years, we're not making the movie in the first place."

Musicians wouldn't retire or stop making albums (or good albums) so readily if they can't rely on evergreen sales of stuff they did 20, 30, 40 years ago.

Etc.

The purpose isn't "Your children should keep earning money from this."

Once upon a time there were no copyrights at all. You created something because you wanted to create it. People still made stuff.