The main arguments for it being a pro military and pro war movie is that the Bugs ARE attacking and that if humanity wants to survive, they will have to fight. Then, while most people do die, the movie ends with a major victory that looks like it may help save humanity.
I don't really think you can argue those points away to claim its an anti military/war movie. The movie would have needed for humanity to have attacked the bugs first, starting the war; or at the least having had most everyone die for no reason, without making a shred of progress in the war effort.
I mean, they were fighting to save our entire species, and the two most vocal people in the entire movie (Ricos parents) that were against the military machine were some of the first people to die in the movie.
Are the bugs really initiating the attacks? Because with the distance between Klendathu & Earth it seems pretty obvious the movie is trying to imply the bugs aren't the ones sending meteors at the humans.
When I rewatched the movie with a friend recently he was surprised that the movie ended with what felt like an anticlimactic resolution - because the war keeps going forever (or so it seems). I really like the interpretation that Starship Troopers (the movie itself) is an in-universe propaganda film used to recruit soldiers to feel important and make a difference in the war effort.
The point is the war must continue for ever, this is made very clear in the book - that's what happens when you deify soldiers, when you make a society obsessed with valour there needs to be a war for the generals to earn stripes - when your society's entire social contract and cohesion is based on war your leaders will always find a war that just HAS to be fought...
The movie point blank says the bugs attacked first and that it's a colonization species that just hurls meteor filled bugs randomly into space in order to try and find new planets to colonize.
Also, when the "main" character in the movie (Rico) is in basic training and about to quit the military, a bug meteor impacts the earth, taking out an entire city, and killing his parents, so the bugs were most definitely attacking humanity, and earth directly.
The movie also ends on a high note, making it seem like they learned some very important information by capturing one of the until then unknown bugs that was able to think and direct all the mindless bugs. So while the war will go on, it leaves the viewer to think that humanity was making progress towards a victory. The movie also marked the first time that humanity actually went to the bug home planet and "took the war to them".
Klendathu is shown to be on the opposite side of the Milky Way. It is physically impossible for the bugs to hurl meteors at these distances while accounting for drift, every piece of matter in between and also the time difference. "Oh yeah, let's launch this meteor so it can destroy a city called Buenos Aires, that hasn't been founded yet by a species that hasn't evolved yet."
They didn't learn anything at the end, they all remained the same characters, still happy to be gears in a military machine. Oh, and NPR mutilated the brain bug's face vagina.
The music made you feel this way, but that's to manipulate you to do so.
It is physically impossible for the bugs to hurl meteors at these distances
This one always bugged me (no pun intended) when I first saw the movie as a kid.
We (humans in the movie) can barely do precision missile-strikes on another planet across the galaxy, and the bugs are way less technologically inferior. How do they even move/manage a meteor?
The bug meteors aren't launched ballistically, they are launched in some kind of superluminal method that isn't explained and doesn't need to be, it did bypass earths defenses however. You can see that happens because the transport ship Denise Richards is piloting literally sees it happen. In the movie the idea of Buenos Aires being a false-flag isn't supported by the text, nor the subtext.
The movie actually doesn't care if the asteroid was sent by the bugs, was a false flag or just really unfortunate circumstances because it doesn't matter. What matters is how the government reacts and the government instantly presents it as an attack.
It's like with WW1 the assassination of Franz Ferdinand is presented as the reason the war started, but really countries were just looking for an excuse to start a war. Buenos Aires didn't really matter because Earth was just looking for an excuse to start a war.
You're missing the satire. It's a satirical anti-war movie. At face value everything in the movie makes sense, the bugs attacked and we're fighting for our survival. But you really need to take a deeper look at the movie. How do we know the bugs attacked first? The government told us. What do we know about the government? The government promotes a militaristic class society where the only way to be a citizen is to join the military. You regularly see people who have lost limbs, how did they lose them? It's not a peaceful society, otherwise people in military service wouldn't lose limbs. You dig and dig and eventually you would have to question what the movie shows you. You can't really be certain that the bugs attacked first because all you know is what the government tells you and that its in the interest of that government to have this war.
And the movie even backdrops that the war effort is not on the side of humanity. Towards the end of the movie roughnecks get reinforced and those reinforcements are literally children. You don't send children as reinforcements unless you're scraping the bottom of the barrel. It's a very clever hint that humanity is actually losing that war.
But none of that changes that during the time frame of the entire movie, humanity is being attacked (regardless of who shot first) and that the Bugs will destroy humanity if they aren't fought against. It's hard to be a movie seen as anti military, when during the time frame of the movie, the only thing saving humanity is the military. Everything else is speculation, like who attacked who, why the war started, if the military machine intentionally started the fight....all of that is just at best a "we don't know".
But what we do know, is that aliens are attacking the earth.
But how do you know humanity is being attacked or that the bugs will destroy humanity? Just like you say everything else is speculation that is also speculation. It's also a speculation that the only thing saving humanity is the military. For all we know we're actually the attackers and bugs are just defending their homes and if we never attack there wouldn't be a conflict.
You can't just take away the whys and hows and say it's pro war. It's satire, if you remove all the nuance then of course it's going to be pro war. The whys and hows make this an anti-war movie.
Buenos Aires, on earth, was destroyed and everyone living there was killed.. nothing within the movie actually presents as the bugs may not be trying to destroy humanity and just spread/populate the galaxy. All of the government conspiracy inside job false flag stuff everyone here has fun talking about is almost completely baseless. It's all conjecture.
There is implications in the film that we started colonizing the bugs territory and initating conflict. We caused the war. The bugs were just defending themselves. While we sent massive ships after their planets.
It's all people who don't read much or only read modern stuff, heinlein was an author who explored ideas he wasn't someone who believed that his job was to tell people what to think. People who think the book is trying to be pro or anti anything are honestly borderline illiterate, they certainly haven't read his other work.
The movie is just a dumbed down action movie directed by someone who didn't really understand or enjoy the book - is a great movie for an action movie but it's not very well thought out and it's certainly not deeply thoughtful.
The film misses all key moments - the first scene, Zim throwing the knife, etc and everything subtle that really makes the story and emotion work - for the film the ending makes no sense, in the book it's really powerful.
The movie isn't really about much, the book is about everything - along side Friday and Stranger it's a fascinating insight into the evolution of Americanism and cultural ideals pushed to absurdity. That's not to say it should be read expecting answers, prime golden era sci-fi wasn't about giving answers it's about posing questions - hence foundation, the laws of robotics series, Stainless steel rat, etc - 'We must be as stealthy as rats in the wainscoting of their society' it's not about telling you how to live or how not to live it's about showing possibilities you probably haven't thought to explore.