No one has a god given right to anything someone else produces, but when it comes to copyrightable works, once you share it with me, you don't have any rights to take it away from me. You may be able to take the physical manifestation of it away from me, but you cannot take the copyrightable portion away. If you didn't want others to have that ability, you shouldn't have shared it with them. That's how ideas (and the expressions of those ideas that are copyrightable) work. It's like nothing else. You can take away all my CDs, computers, sheet music, etc, but you will never be able to take away the song. You can steal my DVDs, but you can't steal the movie. You can burn my books, but you cannot burn the story.
By the very nature of the universe, you do not have to get permission to add something to the public domain. On the contrary, once it is shared publicly, you have to get permission to take it out. That permission is granted by the society you live in through copyrights. We allow you to take works out of the public domain to which it naturally belongs, on the agreement that it will go back after some period of time.
You can argue how long works should be allowed to be taken out of the public domain; you can argue whether they should be allowed to be taken out of the public domain; but you cannot argue whether there should be a public domain. It exists. It is natural, it cannot be taken away, not by law, not by fiat, not by decree, nor by any other means man possesses, unless and until you can change the very nature of the mind.
As for your comments about no incentive to succeed....
You (and a lot of other people here) seem to advocate a system that gives no reward or incentive to succeed. It doesn't seem to matter to you how amazing a work someone produces; the viewpoint I'm reading says they are entitled to the same share as someone else who makes a totally mediocre piece of work.
Right, because James Cameron got the same share as the makers of Pluto Nash.
We, as a society, allow content creators a limited amount of time to take a work out of the public domain. During that time, they have the same opportunity to make money as any other content creator. Some people think that there ought to be opportunities to extend that time, but I've never seen anyone who thinks the time extension should be based on the profitability or popularity of the content. Granted, if the work isn't profitable, the copyright holder will probably not want to pay to extend the copyright terms, but I've seen no extension propositions that prevent it.