You cannot understand the Starship Troopers movie until you realise it is all a propaganda piece.
If you think the Bugs are a threat, you have missed everything.
To understand the movie Starship Troopers it is crucial that you realise the _entire_ movie is propaganda for the Earth's military government. It is clear at the start, and the finish, but it never stops being that a propaganda show.
So nothing can be accepted at face value. Here's what we know:
1. Earth is under control of a military government (a junta)
2. Life is tough: food is rationed, the world is overpopulated
3. You can't have children (or vote) without serving in the military
4. There are dissidents / rebels / those who oppose the one-world order
To keep the population under control, the military leaders need a war. The population will accept hardships, and the excess population can be whittled down. People can be kept busy with work creating disposable goods (bombs, spaceships, uniforms), so they don't have time to think or rebel.
The Bugs are not a threat to humans. They defend themselves. They have no space flight capability. They have no means of attacking Earth. They are a manufactured threat.
Their purpose is to kill as many young people as possible. Young people are a threat to the established order (notice how _old_ the military leaders are). That is why the military strategy is so stupid. The purpose is to get people killed. Population control.
And then grieving relatives at home will continue to support the war.
Because the carnage is so great, people get promoted very quickly. Ignorant, naive young things in command, who will just follow orders.
Finally, we have the giant rocks hurled onto Earth. Bugs? Nah. That's the Earth government. Notice how the rock impacted _directly_ on to the area that was rising up against the military government on Earth?
Multiple birds killed with one (big) stone. Dissidents: vaporised. Support for war: raised amongst survivors. Population: culled. GDP boost: keep people busy rebuilding infrastructure
And THAT'S why the female 'heroine' got such a bollocking for changing course without orders. They nearly got in the way of the rock, and the ship sensors could (did!) log the source. Not the bugs. Humans.
So the sequel is the three friends: one a grunt, one an office, one an 'intellectual'. The first two miraculously survive to figure out what is really going on, go to scientist friend, who betrays them. They go on the run. Carbonite may be involved.
But in the third part, the scientist turns out to be working for them on the inside. he had to betray them to save them. But he's been collecting enough info to blow the whole conspiracy wide open.
And together the three of them overthrow the junta, bring peace and democracy, and an uneasy truce with the bugs. Maybe start some colonies. They all live happily ever after.
(Until the Bell Riots)