Now I'm very confused.
To answer your question: I thought
you were talking about modern copyrights lasting forever. To me, "the Superman copyright should last forever" and "Superman should never enter the public domain" are two statements that mean
exactly the same thing!
If your position is that DC/Warner should have the option of paying to "renew the Superman copyright" at regular intervals, over and over again, with the copyright
never being legally mandated to finally die of old age after a hard-and-fast time limit has been reached, then for all practical purposes isn't that the same as "the copyrights on Superman and other popular 20th Century creations ought to be allowed to last
forever"?
You seem to feel there's a distinction between "Superman should not enter the public domain" and "copyrights should last forever," since you claim you favor the first of those ideas, but don't endorse the second one, but I'm unable to see the distinction.