It was Heinlein taking the “only veterans should be able to vote” to a logical end. A society that’s always at war because the ruling class are all military.

The opening pages tell you the reality - land on planets and nuke the bugs, even if there’s intelligent life there. And use all those nukes, we don’t want to bring those back to the ship. It’s heavy and inefficient.

After that, we step into the eyes of a high school student being indoctrinated.

Heinlein wrote the book extremely well, but many fail to see the whole picture. He didn’t approve nor disapprove. He just took a stance his father had always held and crafted a world where that was the reality.