I’ve often wondered what purpose any aliens would have to invade the Earth. There is no element that you can find on Earth that is not more abundant somewhere else, enslavement seems pretty poor since any race wise enough to transit across solar systems should have the technology to acquire far more efficient workers…namely the robotic kind that don’t produce waste.
Likewise Humans in particular don’t seem like they’d be all that fun to torture or kill, it would make more sense to find a race that isn’t busy murdering its own. You want one that is unified so that the sense of terror is more palpable (I do a lot of character development for tyrants…) Attacking a violent race is boring, you are left with a species that frankly would have likely killed itself off without your help. That’s like trying to assist a computer in calculating something, it was doing quite well on its own.
Also if you are a species that has developed the ability to travel across the universe you’ll likely have terraforming down to a science. Why enter a planet that already has tons of organisms with their own bacteria’s that could easily kill you in hours or days when you could instead start your own relatively clean planet with all your own bacteria that you are used to.
Likewise it would seem smarter to invest on a planet with a younger star than our sun. To optimize the amount of time that a planet can be used. No reason to spend all sorts of time fixing up a planet just to have its star explode in your face a few million years down the road (because I’m hard pressed to think that all sentient species are as obnoxiously present oriented like humans).
As it stands I’m hardpressed to see any reason that any alien would ever, future or past, come to the Earth. Our anus is hardly interesting enough to justify the levels of probing that have been attributed to extraterrestrials and rednecks are only funny the first 2-3 times you meet with them. So I’d say perhaps it is more Jack Daniels than ET leaving people with sore rumps and paranoia.