A week or so ago, scribe_ari
and I were watching some educational TV. The topic was all the ways the Earth could be destroyed. The show presented apocalyptic visions of global war, germs, asteroids, coronal mass ejections, AI running amok, and then I laughed: aliens. Seriously?
They handled it very well. I don't recall the name of the person they interviewed, but he gave an absolutely BRILLIANT explanation of why aliens will never destroy the Earth, nor take any interest in us more than a passing glance. I will expand on his thoughts.
We are primitive. That is it in a nutshell.
Imagine a space faring race from a distance star. It is clear that they have tremendous resources at their disposal. Their technology is so far advanced that we are cave people by comparison. If they can build space craft like that, then they have no need to invade our planet. We would have nothing to offer. Not water, not food, not slave labor.
Food - they would have their own means. They just came from another solar system and I imagine they have the food problem sorted out for a journey that far. If they can travel such great distances in short times (like days) then resupply is simple for them. Water? It would be trivial to make from any nearby gas giant or mine it off of a comet.
Slaves - They have interstellar space craft. Technological capability on that level means that fully automated mass production techniques are at their disposal. This makes the idea of slavers laughable. Why pay for the upkeep and discipline problems of maintaining slaves when you can have a machine do it for you? Slaves are expensive. Even space aliens must have a grasp of basic economics. But a slave is only as good as its intelligence. No one would think of having a chimpanzee build a pyramid. Our primitive technology means even greater investment as the alien masters would have to educate us poor humans to be useful to them. Why would you teach a chimp to use a forklift? How could you?
Trade - They are interstellar. Why bother setting up a trade system with a race that hasn't left their own planet? Just ignore them and take what you want from any of the other planets, comets, or asteroids. As they are an interstellar faring race, they would probably have many other planets to choose from if they need something green and living for their own version of FTD. Some of those planets might even have more advanced civilizations. Technologically, what would we offer them? Ipods? What about tourism? It is unlikely tourism would happen since our race is so primitive by comparison and a good bit of the population actually hostile to "outsiders". That would be like a black CEO showing up with a camera at a backwoods KKK rally to experience the "local culture" and to "rough it". No. No tourists.
War - How many ants can you stomp until you are bored? We pose ZERO threat to any interstellar space faring race. The idea of being caught in the middle of a territorial conflict is also out. Our little sun is just not near anything. In space travel terms, you really have to go out of your way to get here. Earth doesn't even make sense as an outpost.
So there you have it. There is not one reason for a space alien to take anything more than a passing interest in our little planet. The old joke has a bit of truth to it: "the proof that there is intelligent life in space is that it hasn't visited us".