One explanation that's been offered to explain the lack of evidence for extraterrestrial civilizations, even if intelligent life is common in the universe, is that civilizations technologically capable of producing such evidence (e.g., radio transmissions) are likely also capable of destroying themselves through war. The speculation is sometimes formulated as a race between the ability to make contact, or more tendentiously advancing philosophically to a peaceful society, and the ability to self-destruct.
One thought, though, that bothers me (particularly on a night when I can't get to sleep) is what if philosophy does indeed advance and further that nihilism is true, so that philosophers eventually prove it? What if every sufficiently advanced civilization self-destructs deliberately? Stanislaw Lem wrote a story, Fiasko, with a theme not to far from this, where a spaceship is sent to investigate a planet that shows signs of intelligent life but completely refuses all contact.
Then I get a good night's sleep and cheer up, but the thought still worries me a bit. I don't know of any good arguments against nihilism, I only know that humans aren't built to take it seriously unless they're clinically depressed.
Once again, I've pulled part of Camilo's comment up into an entry of its own, so it doesn't get overlooked:
Although there is no logical link between the possibility of Zombiehood, and concluding that if a Zombie can exist, then the rest of humanity must be a Zombie as well.
I think the link is pretty direct, as I'll try to explain.
If you're a physicalist, who believes that mind is just something that happens with the right configuration of matter, then according to your (physicalist) theory the fact that you can observe things exhibiting the appropriate behavior and having the appropriate physical structure counts as evidence that those things have minds1. So there's lots of evidence for other minds.
But if you believe in the possibility of Zombiehood, then explicitly what you disbelieve is that any of that stuff counts as evidence of minds. But if that's the case, what possible reason do you have for supposing that there are any minds except the one and only case for which you do have observations of the type that you think count? It seems to me not at all kosher to help yourself to physicalist intuitions to kick-start a supposition that other minds are a possibility, let alone a probability, while strongly denying the possibility of empirical evidence of the existence of another mind in any specific candidate for Zombiehood. A person who thinks that Zombiehood is at all a live possibility owes some kind of explanation of why the existence of other minds is more than a bare logical possibility, the way other invisible intangible metaphysical entities such as malevolent senses-fooling demons are, and particularly why the rest of humanity is a better candidate than, say, rocks, clouds, glasses of water, or sunlight.
[1] I'm using have a mind to mean experiencing qualia