Is it ethical to exterminate the Aliens?

I got into a weird discussion with a friend of mine. He argued that when Ripley in Aliens encountered the Alien queen and threatened her eggs, the queen backed down, so this proves that she was ready to let Ripley get away and therefore burning the eggs and nuking the complex was essentially unwarranted aggression. The argument then developed into the general question: is it morally permissible to exterminate the Alien race, given the chance? Or is it some misguided application of anthropocentrism gone genocidal? I should be going to bed right now, so naturally, I have to delve into this question. 

We come in peace.

In my opinion, if humanity had the chance, they should wipe out the Aliens. I would not extend this argument to many other species that are dangerous to us humans, for example the Predators or whatever the hell the guys from Independence Day are, or even the apes from Planet of the Apes, despite their wiping us out in the end. Neither would I argue that a simplistic analogy to earthly predators like tigers work. They undoubtedly are dangerous to humans, but wiping them out is a criminal act, as opposed to the Aliens. And, obviously, I have reasons for this. 

Please don't kill me.

The most important - and perhaps only important - reason for this is that the Aliens are an existential threat to humanity that can not be averted. And I know that this is ironic given that I said I wouldn't necessarily exterminate the Indepence-Day-kill-squads. The Alien, in Kyle Reese's words, can't be reasoned with, doesn't feel pity, or remorse, or fear, and it absolutely will not stop, ever, until you are dead. Ash, the Nostromo's android, puts it even more bluntly: It's a perfect organism. Its structural perfection is matched only by its hostility. A survivor... unclouded by conscience, remorse, or delusions of morality. 

From the mouth of robots.

If only one Alien ever gets to earth and hides for a few days, it likely starts a chain reaction that's really hard to contain. The Alien isn't like a tiger, defending its hunting grounds. It's an extermination machine. On LV-426, the Aliens overtake the whole complex in a matter of days, killing everyone except crafty little Newt. No normal predator would do that. And for all their evil ways, the Predators themselves don't wipe out civilizations, because there is no sport in that. There's a decent chance that with the right technology, you can contain the Predators. Or the aliens from Independence Day. Or tigers. Heck, we're actually a bit too good at containing tigers.

The tiger shot first.

The Alien, on the other hand, will multiply and kill, conveniently combining the two. We never see them actually eat anything, by the way. Perfect organisms as they are, they likely don't need food anyway, but that's basically a discussion leading nowhere because the Alien is a creature of nightmare, and nightmares seldom need nourishment. So, what about the Alien Queen and her protection of the eggs? Sure, she refrained from killing Ripley on the spot, but only because she's smart enough to recognize the danger to her offspring. And Ripley, on the other hand, is smart enough to recognize that she didn't conclude a truce with the queen. Right before she threatened to blow up the egg collection, the queen's bodyguards were preparing for an attack. And after Ripley's threat, they simply recede in the shadows. No way they will let Ripley peacefully walk back to that elevator with their treasured price (Newt).

Not coming in peace at all.

So yes, the Aliens are clever enough to know when to beat a retreat, but that's about as far as you can get. So what are your alternatives? You can declare LV-426 a quarantine zone, but whenever you close something, some asshole will want to land on it. And again, as established, one xenomorph is absolutely enough to start the fatal chain reaction on Earth. This is an existential threat that no other alien other than the Alien I can think of poses. And the damn beasts prove in the movies that they can get across ships and even survive in outer space for a time if need be. So if we're sensible, we will not take our chances with them. They surely will not.