You copied much of the Wikipedia entry word-for-word, but managed to skip the following sentence: "Interspersed with the primary plot are classroom scenes in which Rico and others discuss philosophical and moral issues, including aspects of suffrage, civic virtue, juvenile delinquency, and war.

And in the book Heinlein did indeed limit full citizenship to those who'd volunteered for Federal Service. The idea being that only those people have shown that they're willing to put the needs of society over their own.

Was excited to see the film when announced, but disappointed in the final result, as it did Heinlein's work a grave disservice.