Don't Shoot the Message: Although the book suffers from a Broken Aesop by only portraying the liberals as extremists, it doesn't negate how dogmatic both sides of the US political system have become in real life. As he states in the afterword, people in the middle who are reasonable and sane get lumped together with the extremists of whichever side they support, and that modern politicians focus too much on calling out and demonizing the opposing side instead of acknowledging when their side messes up.
Family-Unfriendly Aesop: A benevolent dictator who started a civil war to put himself into power can sometimes be the best man for the job. Card's The Worthing Saga and Songmaster also share this aesop, an apparent author favorite.
Ho Yay: A massive amount with its two protagonists. Ironic, given the author.
Word of God: The afterword where Scott Card speaks about the problems of extremism in the American political system. It's very apt, but is hamstrung by virtue of it following a book that only had one side be at all extreme. And by Card's nonfiction writing about how there needs to be a rebellion in the U.S. over gay marriage.