I love (sarcasm) how a supposedly technologically superior and enlightened species of non-earth intelligent beings would only be out to destroy or punish us, according to science fiction and a lot of people.
Enlightenment and technological superiority don't necessarily go hand in hand. In fact, looking at human history, a lot of technological advancement came directly out of actual or potential warfare. (Remember that the U.S. went to the moon to beat the Russians.)
As Douglas Adams said:
"Man has always assumed that he was more intelligent than dolphins because he had achieved so much...the wheel, New York, wars and so on...while all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man...for precisely the same reason."
You're trying to use humans as an example for the possible disposition and psychology of aliens? Really?
Does it not strike you inappropriate to do so considering the billions of years of evolution and absolutely random events like mass extinctions that led to the rise of mammals and eventually humans?
Humans are the only real evidence we have of how a technological society develops. Evolution produced us, and evolution arises from the physical laws of the universe. Why should we believe it would operate differently elsewhere in the universe?
No planet will have infinite resources, so it's logical that life will develop through continuous competition for territory and materials--just like it did here.
Looking back at Earth's history, it's not like we are the only violent forms of life we know of. Quite the opposite.
Do you remember what happened when the europeans travelled around the world? 90% of populations died from new illnesses. They basically saw nothing ill in settling and displacing the remaining population.
Well, alien illness probably won't kill us. Without a common ancestry, it's highly unlikely that anything that uses an alien as a host can live in our bodies.
We don't know that. There are plenty of examples on Earth of cross-species infections. No telling how microbial/fungal agents could directly attack or indirectly impact the delicate balance here on Earth.
Further, any microbe hitching a ride aboard an alien may well find Earth's general environment to be easy to thrive in. Think Kudzu, but at the microbial level. Eventually, the alien microbe and/or the natural Earth microbes will mutate in order to out-survive the other.
You assume that all life would be carbon based. And even assuming a "super fit" carbon-base alien microbe, the worst you could get would be some kind of eco-disaster that will end up being controlled anyway - like some sort of alien-algae overpopulating our oceans doing some eco-havoc. Even that would involve a kind of "super-fitness" created by an accelerated evolution running for much longer than here on Earth, as this microbe will have to compete with many others that are much more adapted to our environment.
Anything really dangerous, like something that can infect multiple species, would have to be "engineered". "Mother nature" (aka evolution) doesn't engineer bio-weapons made to take over alien ecosystems - you would need huge time spans plus ubiquitous means of interstellar transportation for natural selection to favor such features (think "star gates" but zillions of them with tons of creatures and cargo running through them for at least tens of millions of years).
So I'd take contact with a "non-engineered super infection" like you describe as a sign that someone has been operating a huge network of interstellar transportation systems for quite some time, as this would provide the only "peacefull" evolutionary history (again, excluding civilizations expert in bio-war things...) for such thing to evolve, so it would be quite a good omen for hopes "intergalactic fraternity" :)
The possibility of non-carbon based life is so remote as to be irrelevant. We'd have to go through many star birth and supernovae cycles to get to the point where silicon is even anywhere near as abundant as carbon is now.
As for microbes from other worlds, who knows. The properties of water are pretty much required for life (as far as we know) and so they'd have 0 trouble interfacing with most organisms. Combine that with the fact that the basic amino acids can form in a wide range of conditions and you've got the recipe for interference. Also, infections happen when organisms invade and multiple, some times the damage is a secondary side effect (i.e. waste or toxic byproducts)
Name the occurrence in the history of our planet where the much-more advanced/capable species did not displace and diminish the indiginent one. In many cases, the more advanced or aggressive species completely wiped out the existing one.
There's a lot more that's extremely unlikely in the Star Trek universe besides just transporter beams and faster-than-light travel.
A sufficiently advanced species might not feel any more compunction about eradicating the human race than I would feel about eradicating mosquitoes.
Humans and buffalo. Humans and passenger pigeons. Humans and mastodons. Humans and elephants. Humans and tigers. Humans and smallpox. Humans and dodos. Etc.
No, I just wanted to make sure you weren't conflating what happens to species with what happened with Columbus and Hispaniola. I'm not so sure we know in enough detail exactly what happened to Neanderthals for that to be a good example, especially since the conversation is about the meeting of different civilizations, not just different species.
They might not be out to destroy or punish us. They might take no more interest in us than we took in thousands of species that have been destroyed to make way for farms and shopping malls. Maybe our planet would make a good Vogon parking lot.
