Of course the entire genre of cosmic horror is reactionary by its very nature, except when there is enough self-awareness to subvert or satirize the genre's reactionary logic, as in Verhoeven's Starship Troopers. But James Cameron's Aliens has no interest in self-critique, sharing a lot more in common with Heinlein's original novel.
Xenomorphs have only ever defended themselves from human colonizers invading their home, but we're expected to see them as evil, the scary other. The aliens must be bad because they pose a threat to us. Oh, and because they're ugly.
At least in the first Alien, the human crew members are sympathetic because they are merely surviving a situation they didn't want to be in, put in peril by a corporation sacrificing them for profit. Humans, not aliens, are the true villains of the film.
But in Aliens, our hero Ripley goes back to the moon with a special team of Colonial Space Marines to kick some alien ass. While this is ostensibly a mission to save a group of endangered colonists, Ripley has no interest in a search-and-rescue mission. She only agrees on the condition that they go there to kill every last Xenomorph.
Ripley is more than willing to exterminate an entire species to save one little white girl with blonde hair and blue eyes. In fact she still wants to genocide them even after safely escaping.
Ripley: I say we nuke the entire site from orbit, it's the only way to be sure
Burke: This is clearly an important species we're dealing with, and I don't think that we have the right to arbitrarily exterminate them.
Ripley: Wrong!
be sure of what, Ripley? you can just fucking leave. don't go back to the moon with all the Xenomorphs on it. seems pretty easy to me
now of course it turns out that Burke doesn't actually care about the Xenomorphs, he only wants to exploit them for profit. while this is keeping with the corporations=bad theme from the first movie, now we're supposed to think corporations are bad for... not wanting to do genocide? because of course no good person would be against murdering an entire species for no reason, only a villain would propose such a thing.
Now I'm not saying you can't enjoy Aliens, it deserves its status as one of the best action / sci-fi films of all time, and I'd argue these problematic reactionary themes actually make it more interesting and morally complex, giving us much to analyze and critique, elevating it above an average popcorn movie. Just please don't take it at face value.
Ripley is no longer the hero, even if she's portrayed as one. In Alien she is the scratched liberal, and in Aliens she is the fascist who bleeds. In a tragic turn, she has become the villain of the story. She reacts to her own trauma and loss of motherhood with mass murder, by killing another mother's babies right in front of her, and we're all supposed to clap and cheer, instead of asking why these humans are there in the first place.
I'm showing my age here but here but I thought the two most common readings of the film were:
The military at the behest of the MIC get sent into a situation that they have little to no understanding of which results in many good men and women dying, all because the powers that be think that they can turn a profit. Only by banding together can the working class (human or android) survive this situation
(And when viewed it this light, Avatar can be seen as more a refinement of James Cameron's anti-war views than a 180.)
Ripley, the lone survivor of the Sexual Assault Monster is forced/blackmailed by the Patriarchy(Burke) into confronting said monster because the Patriarchy wants to profit off of it, and then the Patriarchy is
face when they find out that they can't control the Sexual Assault Monster and gets sexually assaulted. Only by building a coalition of feminist allies and confronting her trauma head on (with a power loader) can Ripley prevent the same trauma that was inflicted on her from being inflicted on the next generation.
I've heard the Vietnam metaphor before, and I think it pretty much supports my thesis since that would make Ripley a volunteer soldier in the US military who decides to nuke North Vietnam because a few of her fellow soldiers got killed - and uhh to be clear I am not into the idea of likening Xenomorphs to Vietnamese people obviously but if that's what the movie was going for then it seems very reactionary indeed
The reason you can't go "Xenomorphs are a 1-to-1 allegory for the Viet Cong" is the same reason you can't just say that the movie is reactionary and pro-genocide: the Alien is too big and all encompassing a metaphor for how uncaring and hostile nature is in the face of human endeavour. It's not just a simple Other, it's the face of annihilation; it's a WMD found in the wild the same way Uranium or Anthrax is.
Ripley's argument that the Xenomorphs need to all be destroyed is the same argument for the destruction of all samples of deadly diseases that can be used as biological weapons: it is too inimical to human life to be allowed to exist, especially because the MIC keeps trying to weaponize it in order to profit off of it.