Sorry for the late reply. I admit I haven’t read the book and thus can’t comment on it, but the movie is a great commentary on fascism, because it surprises us by making us notice that “Wait a second, I’m rooting for the fascists. How did that happen?!”. The visual messaging is pretty clear with the giant eagles, Hugo Boss leather uniforms and overall militarlism and xenophobia, but it goes much deeper than that.

Everyone gets free healthcare and education, as long as you’re part of ‘us’ instead of ‘them’. We’re used to the fascism where ‘us’ is some ethnic or religious group of humans and ‘them’ is some different group of humans. In starship troopers however, the fascism gets to fly under the radar by making the entirety of humanity the in-group. The aliens don’t need to be dehumanized because they’re quite clearly not human. Yet they feel fear and are only reacting to the spread of humans into their neighbourhood, while humans are outright shouting for genocide. “The only good bug is a dead bug!”

Wisecrack made a good breakdown of this a while back.