Do you believe in extraterrestrial life?
Absolutely. And not only do I believe it exists, but I believe the universe is teeming with it. I would even go so far as to say that life is not only a by-product of the universe, but even moreso a requirement of it. Do I believe we've been visited by extraterrestrials? As much as I'd like to say yes, now I have to say probably not.
I love a good UFO/alien abduction tale as much as the next guy, but while it's not impossible, considering the distances involved and the technology required for interstellar flight it's all very, very unlikely. And on top of that, after spending the last 50 or so years observing humanity on this planet, I have come to the conclusion that if extraterrestrials are anything like us, as soon as they start taking their first tentative steps out of the nest, 99.9% of them either self-destruct over cultural differences and god-myths, or are wiped out by natural forces beyond their control. The threat posed by rogue asteroids, comets, gamma ray bursts, catastrophic climatic change, super volcanoes and tectonic shifts certainly are not unique to the Earth, but ultimately I believe the risk of them wreaking planet-wide destruction is miniscule compared to the amount of havoc that can be unleashed by a civilization upon itself, either intentionally or through blind stupidity.
And what of the 0.1% of technological civilizations that do survive and achieve interstellar spaceflight? I think they would be so different from us as to be virtually unrecognizable, and totally uninterested in Homo sapiens in any capacity, having seen the path we're heading down play itself out thousands of times before.