I don’t think that is what would happen.

If your have the technology for interstellar travel, why would you need slaves? Interstellar travel implies you have automation, automation means slavery, outside of just being cruel, is obsolete.

If you have superior technology, you’d likely be knowledgeable about the other parts of science and know that you may carry germs that are harmless to you but dangerous to us. They’d likely have learnt this the hard way, like we have.

Also, why would thier first reaction to new life be “Exterminatus”? That ship suggests high technology, high technology suggests science, science suggests curiousity. A lot of the people who say “they’ll exterminate us like rats” either have watched too much sci fi or have a cursory knowledge of history. As someone who actually has history qualifications the reason Columbus killed so many people was because:

1. He was a greedy bastard who valued Gold in a way the Natives did not.
2. He was a psycho who believed that if he didn’t get what he wanted the best reaction was violence so hard that his own government imprisoned him for what he did.
3. He was a religious nut looking to convert people and recruit them for a fucking crusade.

Man was a psycho by the standards of his time, but that’s not to say more horrific things weren’t done in the name of economics.

The factors that drove the imperialists of the new world wasn’t “lol just because”, it was mainly capitalism and the need to extract labour from the populace for their own financial gain. In short. Resource extraction driven by the desire for power. Now that’s scary, but we’re assuming these aliens are driven by the same economic factors.

Ok. So let’s assume that somehow the aliens want resources. They gonna get them from Earth? Well, there is nothing here that isn’t found in greater abundance in our asteroid belt or moons bar cultural products or products of life, and most of those will likely not be compatible with them. The earth is far more valuable as something to study, you know, because it’s an independent ecosystem with a technological civilisation, they xeno-biologists and xeno-anthropologists would be all up in that while the rest of the fleet mine asteroids in the belt

Think of it this way. You’re out in the woods, and you see a crow hop across your path, take a twig, and hop back. As your eye follows the crow you see smoke, like from a small campfire. You go into the bush towards the smoke and you find a collection of thatched roof and mud structures about waist high to you and loads of crows living in them. There’s a crow in the background with a little stone hammer building something, another seemingly in the process of smoking fish, and yet more doing various tasks. Is your reaction going to be “they don’t have smartphones so they’re worthless”? No! Your reaction is going to be 'Holy shit, crow village" and you’re going to alert the university because the crows have gone from the early stone age to the fucking Bronze age.

I don’t think the reaction of aliens will be like us to chimps, even if it was, we study chimps, their reaction would likely be “holy shit, they’re sending probes out, they’re doing science” because if a species is too dumb to recognise a fucking space probe as technology, they’re too dumb to actually make it to space.