No, I am using the language of current legal system (which recognized IP) because otherwise I have to establish an alternative context. Again, the language is being used, but the underlying purpose behind the law is not being respected.

We can imagine a society where copyright laws don't exist, i.e. content created by someone is not considered their property and others may do what they will with the content in a GPLisque manner. In that society we would never have to use 'my/their content', as there will be no notion of IP in that society.

People would be free to make use of the creative expressions of others, yes, but it would be more like MIT/BSD than GPL. All else equal, anyone would be free to make a modified Linux and publish the compiled binary without being required to publish the source code. What you describe would require not only abolition of copyright law but also a new copyleft law.