I guess Warner's point is..

Warner’s point is an individual becomes subject when he or she enters the public sphere. He says “public opinion is understood as belonging to a public rather than to scattered individuals. So it is only meaningful to speak of public discourse where it is understood as the discourse of a public rather than as an expansive dialogue among separate persons.” In order to do that, he suggests people to be idealized public speaker, identified as self-abstraction. , that represent people. When they voice opinion in counter sphere, they are not private individual anymore.

Even after I read the Warner's writing, I couldn't understand his point. So, I put "guess" on the title. I do not like to read that kind of complicate writing that make the point ambiguous and hard to understand.