it consists of basically the same joke over and over again: military people are evil and stupid.
I didn't see it that way at all. Sure, the book was about military people, and most of them were stupid and some were evil. But I took the point to be not that "military people are evil and stupid," but rather that many people are evil and stupid and that if you put these people into the military they will continue to act that way, with potentially horrible consequences. So it's not an insult directed at military people, but a commentary on the inevitable consequences of placing ordinary people at war.
He also says:
Satire always has an intellectual point. The point here seems to be that war is a bad thing.Again, that's not how I saw it. I thought his point was that from the individual low-ranking soldier's point of view, war is going to seem pretty awful. That doesn't mean that all wars are bad from a broader perspective. It just means that having to kill and possibly be killed is an awful experience.