Kinda tangential to Aliens, I guess, but while thinking about Starship Troopers in its entirety, meaning 1, 2, Marauder, Invasion, and Traitor of Mars, it occurs to me that the fundamental weakness of the setting is that the Bugs are always the violent monsters that preclude the idea of diplomacy. Now, Marauder is the Steelman example of Verhoeven's vision even though he didn't direct it because the Federation actually do act like Fascists in it with its brutal suppression of political dissent, blatantly false propaganda, having an actual incompetent Sky Marshall there for PR purposes, and willingness to sacrifice loyal officers like Col. Rico for political reasons. Now, what do the Bugs do in this movie? The captured Brain Bug tries to perform a big brain maneuver by psychically attacking MI leadership while the Bug God brainwashes the Sky Marshall to manipulate him into believing peace is possible which led to the Bugs storming the base at the beginning of the movie. In Traitor of Mars, the Bugs invade Mars and while the Sky Marshall is a vain bitch that got overthrown for creating the false flag, it still doesn't change the fact that the Bugs are on Mars.
The result is that the Fascist society is necessary. It often has questionable leadership at the very top, but because the Bugs are a constant existential threat to humanity, they don't have any choice but to stick with this government. Those protestors in 3 wanted the war to end sure, but there's no way their hypothetical reforms or overthrow of the MI would have ended the war with the Bugs. Humanity would still be at war with the Bugs regardless of who's in charge.