And we all know that alien force fields are impenetrable by nuclear bombs, so I see nuclear war as an unlikely answer to their lack of survival skills. More likely is their rapid consumption of non-reproducible recourses

You could argue the same for aliens, we are constantly searching for an intelligent technical alien civilization and haven’t found one. But there are about half a trillion suns in our galaxy alone, and we don’t know which ones to look at. We just finally found the first planet in a “habitable zone” LAST YEAR ( http://en.wikipedia.org/wiki/Gliese_581_c ). So we are really just getting started at even finding where to look. After we find it, whether it is in 5 years or 1000 we will say, well shit that was stupid of course there is life, look how big the Universe is.

The problem of if we will find it was best summed up in Carl Sagan’s Cosmos:

“It is very hard to be sure. There may be severe impediments to the evolution of a technical civilization. Planets may be rarer than we think. Perhaps the origin of life is not so easy as our laboratory experiments suggest. Perhaps the evolution of advanced life forms is improbable. Or it may be that complex life forms evolve readily, but intelligence and technical societies require an unlikely set of coincidences – just as the evolution of the human species depended on the dmise of the dinosaurs and the ice-age recession of the forests in whose trees our ancestors screeched and dimly wondered. Or perhaps civilizations arise repeatedly, inexorably, on innumerable planets in the Milky Way, but are generally unstable; so all but a tiny fraction are unable to survive their technology and succumb to greed and ignorance, pollution and nuclear war.”

Sadly, from our experience his last point seems the most probable.

In my opinion is that a persons worldview is also their reasoning (or lack of reasoning). People want to believe ghosts exist because that means there is an afterlife and therefore they live on forever, god thinks they are special etc. etc. Whereas if aliens exist, maybe they are not really special, maybe Earth or Sol is not the centre of the universe. Sometimes peoples irrationality leads them to reject possible existence of aliens and sometimes peoples irrationality leads them to believe aliens are only interested in what is up their bum.