The book is fine. The opening pages tell us clearly that we are nuking bugs on planets with intelligent beings, using all the ammo (because it's too expensive to return with nukes) and leaving for another planet with bugs.
After that we jump to our protagonist, who is being brainwashed in high school.
Finally, Heinlein was writing his father's worldview and wanted to take it to its logical end.
I love that book and movie.