They’re pissed that the airing of the series finale of Single Female Lawyer was interrupted by technical problems.
Like susan said. Pick your favourite First Nations people and picture them asking that same question as Jacques Cartier/James Cook/some Basque whaler pulls up on the shore…
We are our own worst nightmare…
Water. They want our water. They’re only going to take half of it.
Hey, come on. You guys aren’t really using it.
Its possible that the invaders are a shell of a once great empire, either on the run from some unknown horror or dwindling from conflict within- while their technology is beyond ours, they themselves might be creeping back to their ‘stone age’ and need the resources/proximity that Earth offers.
We often see aliens as technologically beyond ourselves, but don’t frequently think of their own advancement within their own culture. Maybe they were even more formidible eons ago? Who knows? Obviously the Little Green Men that come down in their dinged and sputtering UFOs don’t want to let on that their own civilization is in the shitter and they need to punk on a race even more backwards than they are.
Aliens have often been a metaphor for the darker aspects of humanity. Much of the terrible things aliens do in stories are really just reflections of what people have done in the past. By posing them as something foreign (aliens from a distant star) we can objectively see the barbarism of those types of actions.
Some possibilities.
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Already mentioned, the generation ship that is committed to colonizing this system.
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Earth’s ecosystem. Even if the aliens are so alien that all they have in common with terrestrial life is breathing oxygen, that still makes Earth more habitable than 99.99+% of the galaxy. And unless they’re good at building HUGE space habitats, the sheer size of Earth’s ecosystem makes it more viable than any smaller, artificial habitat. Also, the possible value of Terran biochemistry, etc.
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Maybe <gulp> it’s US they’re after! Maybe sentients make useful slaves, not as manual laborers but as suitably controlled processing units- think Borg, or the Matrix.
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Already mentioned, purely ideological reasons. One I’ve mentioned in the past is the idea of a race of sentient herbivores who regard flesh eaters as a demonic stain upon creation, to be wiped out wherever discovered.
I just don’t buy that one. I cannot believe that a society with the technological ability to built massive FTL ships is going to have any use for us as slaves. It would be like the 21st-century United States conquering bushmen to steal their pointed sticks.
Let’s not forget the pre-emptive defensive reason: The aliens perceive humanity as a potential threat, and are taking action, now to control the threat by enslaving humanity, or integrating humanity into their government. (ETA: or simply extermination.) Certainly that has been used as a reason for many conflicts in our history.
Of course, there’s nothing to say that the perception of threat need to be realistic.
Where better to check out that nifty anal probe technology they have developed?
In which case they’d nuke us from orbit.
Well, you guys. I’d have relocated to Brigadoon with Kim & 9998 other couples to restart humanity. There’s seven dopers on the list, but you guys don’t need to know about that know.
I always assumed that an alien “invasion” would be more like the Vorgon’s from Hitchhikers Guide than ID4 or War of the Worlds. Basically, blowing up the Earth or otherwise fucking it up to make way for a “hyperspace bypass” or some other alien agenda completely incomprehensible to us.
Remember Mark Twain’s quip about helpful invaders? “if someone comes to you, with the evident intention of doing you good, you should RUN for your life!”?
I think a beneficient race of aliens would destroy us, as surely as the bad ones would.
To get more Chuck Berry recordings.
Both you and Mr. Twain are paranoid. There’s been a benevolent, godlike alien in Metropolis for going on 70 years now, and the city has suffered no ill effects whatsoever.
Except for all the alien invasions & natural disasters and interdimensional demon attacts & stuff. And that one time the BGA’s billionaire ex-boyfriend ground the whole city to rubble because he was jealous the BGA had gotten married to some snoopy reporter.
Their mom saw the phone bill from calling Orion slave girls and sent them to time out in another galaxy.
I don’t see a reason why they would invade, but I do see a reason to make contact. Presumably if they are out exploring the cosmos to begin with, it is out of curiosity. Finding life instead of just another rock around another sun would probably be worthy of a bit more investigation, much in the same way humans continue to explore our own world in search of new species.
Or, perhaps, the Earth holds clues to the past much like fossils. If we are the result of alien seed, perhaps the life on Earth will provide clues to that history.
Perhaps they just want to serve man.
Dunno. Ask the Native Americans and see if they have any comments. 
Programming/instinct perhaps. Such as a bunch of xenoformers that intend to remake Earth in the image of their homeworld’s creators, or a robotic army sent to conquer all the galaxy for the long-dead Zyrgrex Empire, or a genetically engineered “Master Race” that has the urge to conquer built in, and so on.
They want our resources because they want ALL the resources in the solar system. They want to rebuild it into a Dyson Sphere or something on a similar scale. But for whatever reason - scruples, or a need for zoo animals - they don’t want to simply exterminate humanity, so they land to grab us instead of just dismantling Earth for raw material with us on it.
Because it’s fun. People have done things like burn down villages for fun; I recall reading of a man with a musket and a lot of ammo that boated down a river passing between Indian villages on the shores, killing dozens just because he could.
I’ve pondered this myself, and could never come up with a “practical” reason to invade. The most common idea seems to be that the aliens want our resources, but that doesn’t make sense to me – it seems like the cost (in energy and resources) of hauling everything back to your homeworld would outweigh any benefit. Plus, I have a hard time believing that a super-advanced race with FTL travel would find themselves in dire straits because they’re running out of coal and wood.
I think the most likely explanation would be cultural – the aliens just like conquest. Perhaps they’re xenophobes who feel the need to exterminate other life, or they view themselves as a superior civilization that needs to “civilize” other races.
7 billion men & women, plus a few Dolphins & a little onion, are what they need to make a meatloaf.
They need more raw materials for Glagnar’s Human Rinds (A Muncha-Cruncha-Buncha-Human! Try our New, Improved Barbecue flavour!)
Either that, or they want to test cosmetics or something